Matthew 18:6

If anyone causes one of these little ones - those who believe in me - to stumble, it would be better for them to have a large millstone hung around their neck and to be drowned in the depths of the sea.

A T Robertson
These little ones (tōn mikrōn toutōn). In the same sense as “one such little one” above. The child is the type of believers.
A great millstone (mulos onikos), literally, “a millstone turned by an ass.” The upper millstone was turned by an ass (onos). There were no examples of the adjective onikos (turned by an ass) outside the NT until the papyri revealed several for loads requiring an ass to carry them, stones requiring an ass to move them, etc. Deissmann (Light from the Ancient East, p 81) notes it also in papyri examples about the sale of an ass and tax for an ass’s burden of goods.
The depth of the sea (tōi pelagei tēs thalassēs). “The sea of the sea.” Pelagos probably from plēsso, to beat, and so the beating, splashing waves of the sea. “Far out into the open sea, a vivid substitute for eis tēn thalassan” (McNeile).

Matthew Henry

Those that thus humble themselves will be afraid,
[1] That nobody will receive them; ... verse 5

[2] They will be afraid that everybody will abuse them; the basest men delight to trample upon the humble; Vexat censura columbas - Censure pounces on doves. This objection he obviates (6), where he warns all people, as they will answer it at their utmost peril, not to offer any injury to one of Christ's little ones. This word makes a wall of fire about them; he that touches them, touches the apple of God's eye.
Observe, First, The crime supposed; offending one of these little ones that believe in Christ. Their believing in Christ, though they be little ones, unites them to him, and interests him in their cause, so that, as they partake of the benefit of his sufferings, he also partakes in the wrong of theirs. Even the little ones that believe have the same privileges with the great ones, for they have all obtained like precious faith. There are those that offend these little ones, by drawing them to sin (1Co 8:10, 11), grieving and vexing their righteous souls, discouraging them, taking occasion from their mildness to make a prey of them in their persons, families, goods, or good name. Thus the best men have often met with the worst treatment in this world.
Secondly, The punishment of this crime; intimated in that word, Better for him that he were drowned in the depth of the sea. The sin is so heinous, and the ruin proportionably so great, that he had better undergo the sorest punishments inflicted on the worst of malefactors, which can only kill the body.
Note, 1. Hell is worse than the depth of the sea; for it is a bottomless pit, and it is a burning lake. The depth of the sea is only killing, but hell is tormenting. We meet with one that had comfort in the depth of the sea, it was Jonah (Jon 2:2, 4, 9); but never any had the least grain or glimpse of comfort in hell, nor will have to eternity.
2. The irresistible irrevocable doom of the great Judge will sink sooner and surer, and bind faster, than a mill-stone hanged about the neck. It fixes a great gulf, which can never be broken through, Lk 16:26. Offending Christ's little ones, though by omission, is assigned as the reason of that dreadful sentence, Go ye cursed, which will at last be the doom of proud persecutors.

Matthew 17:20

He replied, “Because you have so little faith. Truly I tell you, if you have faith as small as a mustard seed, you can say to this mountain, ‘Move from here to there,’ and it will move. Nothing will be impossible for you.”

Matthew Henry
... Christ gives them two reasons why they failed.
(1) It was because of their unbelief, Mat 17:20. When he spake to the father of the child and to the people, he charged it upon their unbelief; when he spake to his disciples, he charged it upon theirs; for the truth was, there were faults on both sides; but we are more concerned to hear of our own faults than of other people's, and to impute what is amiss to ourselves than to others. When the preaching of the word seems not to be so successful as sometimes it has been, the people are apt to lay all the fault upon the ministers, and the ministers upon the people; whereas, it is more becoming for each to own his own faultiness, and to say, “It is owing to me.” Ministers, in reproving, must learn thus to give to each his portion of the word; and to take people off from judging others, by teaching all to judge themselves; It is because of your unbelief. Though they had faith, yet that faith was weak and ineffectual. Note, [1] As far as faith falls short of its due strength, vigour, and activity, it may truly be said, “There is unbelief.” Many are chargeable with unbelief, who yet are not to be called unbelievers. [2] It is because of our unbelief, that we bring so little to pass in religion, and so often miscarry, and come short, in that which is good.
Our Lord Jesus takes this occasion to show them the power of faith, that they might not be defective in that, another time, as they were now; If ye have faith as a grain of mustard-seed, ye shall do wonders, Mat 17:20. Some make the comparison to refer to the quality of the mustard-seed, which is, when bruised, sharp and penetrating; “If you have an active growing faith, not dead, flat, or insipid, you will not be baffled thus.” But it rather refers to the quantity; “If you had but a grain of true faith, though so little that it were like that which is the least of all seeds, you would do wonders.” Faith in general is a firm assent to, a compliance with, and a confidence in, all divine revelation. The faith here required, is that which had for its object that particular revelation by which Christ gave his disciples power to work miracles in his name, for the confirmation of the doctrine they preached. It was a faith in this revelation that they were defective in; either doubting the validity of their commission, or fearing that it expired with their first mission, and was not to continue when they were returning to their Master; or that it was some way or other forfeited or withdrawn. Perhaps their Master's absence with the three chief of his disciples, with a charge to the rest not to follow them, might occasion some doubts concerning their power, or rather the power of the Lord with them, to do this; however, there were not, at present, such a strong actual dependence upon, and confidence in, the promise of Christ's presence with them, as there should have been. It is good for us to be diffident of ourselves and of our own strength; but it is displeasing to Christ, when we distrust any power derived from him or granted by him.
If ye have ever so little of this faith in sincerity, if ye truly rely upon the powers committed to you, ye shall say to this mountain, Remove. This is a proverbial expression, denoting that which follows, and no more, Nothing shall be impossible to you. They had a full commission, among other things, to cast out devils without exception; but, this devil being more than ordinarily malicious and inveterate, they distrusted the power they had received, and so failed. To convince them of this, Christ shows them what they might have done. Note, An active faith can remove mountains, not of itself, but in the virtue of a divine power engaged by a divine promise, both which faith fastens upon.
(2) Because there was something in the kind of the malady, which rendered the cure more than ordinarily difficult (Mat 17:21) ....

John Gill
remove hence to yonder place, and it shall remove: meaning, not that it would be ordinarily or ever done in a literal sense by the apostles, that they should remove mountains; but that they should be able to do things equally difficult, and as seemingly impossible, if they had but faith, when the glory of God, and the good of men, required it. So that it does not follow, because the apostles did not do it in a literal sense, therefore they could not, as the Jew insultingly says; since it was meant that they should, and besides, have done, things equally as great as this, and which is the sense of the words. So the apostle expresses the faith of miracles, by "removing mountains", 1 Co 13:2 ie by doing things which are difficult, seem impossible to be done: wherefore Christ adds, and nothing shall be impossible to you; you shall not only be able to perform such a wonderful action as this, were it necessary, but any, and everything else, that will make for the glory of God, the enlargement of my kingdom and interest, the confirmation of truth and the good of mankind.

Matthew 16:24

Then Jesus said to his disciples, “Whoever wants to be my disciple must deny themselves and take up their cross and follow me.

A T Robertson
Take up his cross (aratō ton stauron autou). Pick up at once, aorist tense. This same saying in Mat 10:38, which see. But pertinent here also in explanation of Christ’s rebuke to Peter. Christ’s own cross faces him. Peter had dared to pull Christ away from his destiny. He would do better to face squarely his own cross and to bear it after Jesus. The disciples would be familiar with cross-bearing as a figure of speech by reason of the crucifixion of criminals in Jerusalem.
Follow (akaloutheitō). Present tense. Keep on following.

John Calvin
Then Jesus said to his disciples. As Christ saw that Peter had a dread of the cross, and that all the rest were affected in the same way, he enters into a general discourse about bearing the cross and does not limit his address to the twelve apostles, but lays down the same law for all the godly. We have already met with a statement nearly similar (10:38) but in that passage the apostles were only reminded of the persecution which awaited them, as soon as they should begin to discharge their office; while a general instruction is here conveyed, and the initiatory lessons, so to speak, inculcated on all who profess to believe the gospel.
If any man will come after me. These words are used for the express purpose of refuting the false views of Peter. Presenting himself to every one as an example of self-denial and of patience, he first shows that it was necessary for him to endure what Peter reckoned to be inconsistent with his character, and next invites every member of his body to imitate him. The words must be explained in this manner: “If any man would be my disciple, let him follow me by denying himself and taking up his cross, or, let him conform himself to my example.” The meaning is, that none can be reckoned ... disciples ... unless they are true imitators of him, and are willing to pursue the same course.
He lays down a brief rule for our imitation, in order to make us acquainted with the chief points in which he wishes us to resemble him. It consists of two parts, self-denial and a voluntary bearing of the cross. Let him deny himself. This self-denial is very extensive, and implies that we ought to give up our natural inclinations, and part with all the affections of the flesh, and thus give our consent to be reduced to nothing, provided that God lives and reigns in us. We know with what blind love men naturally regard themselves, how much they are devoted to themselves, how highly they estimate themselves. But if we desire to enter into the school of Christ, we must begin with that folly to which Paul (1 Cor 3:18) exhorts us, becoming fools, that we may be wise; and next we must control and subdue all our affections.
And let him take up his cross. He lays down this injunction, because, though there are common miseries to which the life of men is indiscriminately subjected, yet as God trains his people in a peculiar manner, in order that they may be conformed to the image of his Son, we need not wonder that this rule is strictly addressed to them. It may be added that, though God lays both on good and bad men the burden of the cross, yet unless they willingly bend their shoulders to it, they are not said to bear the cross; for a wild and refractory horse cannot be said to admit his rider, though he carries him. The patience of the saints, therefore, consists in bearing willingly the cross which has been laid on them. Luke adds the word daily ... which is very emphatic; for Christ’s meaning is, that there will be no end to our warfare till we leave the world. Let it be the uninterrupted exercise of the godly, that when many afflictions have run their course, they may be prepared to endure fresh afflictions.

Matthew 15:11

What goes into someone’s mouth does not defile them, but what comes out of their mouth, that is what defiles them.

A T Robertson

This defileth the man (touto koinoi ton anthrōpon). This word is from koinos which is used in two senses, either what is “common” to all and general like the Koiné Greek, or what is unclean and “common” either ceremonially or in reality. The ceremonial “commonness” disturbed Peter on the housetop in Joppa (Acts 10:14). See also Acts 21:28; Heb 9:13. One who is thus religiously common or unclean is cut off from doing his religious acts. “Defilement” was a grave issue with the rabbinical ceremonialists. Jesus appeals to the crowd here:
Hear and understand (akouete kai sunietei) He has a profound distinction to draw. Moral uncleanness is what makes a man common, defiles him. That is what is to be dreaded, not to be glossed over. “This goes beyond the tradition of the elders and virtually abrogates the Levitical distinctions between clean and unclean” (Bruce). One can see the pettifogging pretenders shrivel up under these withering words.

Matthew Henry
The truth itself laid down (15:11) in two propositions, which were opposite to the vulgar errors of that time, and were therefore surprising.
1. Not that which goes into the mouth defileth the man. It is not the kind or quality of our food, nor the condition of our hands, that affects the soul with any moral pollution or defilement. The kingdom of God is not meat and drink, Rom 14:17. That defiles the man, by which guilt is contracted before God, and the man is rendered offensive to him, and disfitted for communion with him; now what we eat, if we do not eat unreasonably and immoderately, does not this; for to the pure all things are pure, Tit 1:15. The Pharisees carried the ceremonial pollutions, by eating such and such meats, much further than the law intended, and burdened it with additions of their own, which our Saviour witnesses against; intending hereby to pave the way to a repeal of the ceremonial law in that matter. He was now beginning to teach his followers to call nothing common or unclean; and if Peter, when ... bid to kill and eat, had remembered this ... he would not have said, Not so, Lord, ....
2. But that which comes out of the mouth, this defiles a man. We are polluted, not by the meat we eat with unwashen hands, but by the words we speak from an unsanctified heart; thus it is that the mouth causeth the flesh to sin, Ecc 5:6. Christ, in a former discourse, had laid a great stress upon our words (Mat 12:36, 37); and that was intended for reproof and warning to those that cavilled at him; this here is intended for reproof and warning to those that cavilled at the disciples, and censured them. It is not the disciples that defile themselves with what they eat, but the Pharisees ... with what they speak spitefully and censoriously of them.
Note, Those who charge guilt upon others for transgressing the commandments of men, many times bring greater guilt upon themselves, by transgressing the law of God against rash judging. Those most defile themselves, who are most forward to censure the defilements of others.

John Gill
Some scruples, about some of these things, did arise among the first Christians; but in process of time these difficulties were got over: nor is there any religion in abstinence from any sort of food; men, indeed, on a "physical" account, ought to be careful what they eat and drink, but not on a religious one; moderation in all ought to be used; and whatever is ate or drank, should be received with thankfulness, and done to the glory of God, and then no defilement can arise from hence ...

Matthew 14:27

But Jesus immediately said to them: "Take courage! It is I. Don’t be afraid."

Matthew Henry

How these fears were silenced (v :27). He straightway relieved them, by showing them their mistake; when they were wrestling with the waves, he delayed his succour for some time; but he hastened his succour against their fright, as much the more dangerous; he straightway laid that storm with his word ....

[1] He rectified their mistake, by making himself known to them, as Joseph to his brethren; It is I. He does not name himself ... to these disciples it was enough to say, It is I; they knew his voice, as his sheep (Jn 10:4), as Mary Magdalene, Jn 20:16. They need not ask, "Who art thou, Lord? Art thou for us or for our adversaries?" They could say with the spouse, It is the voice of my beloved, (Song 2:8, 5:2). True believers know it by a good token. It was enough to make them easy, to understand who it was they saw.
Note, A right knowledge opens the door to true comfort, especially the knowledge of Christ.

[2] He encouraged them against their fright; It is I, and therefore,

First, Be of good cheer; tharseite - “Be courageous; pluck up your spirits, and be courageous.” If Christ's disciples be not cheerful in a storm, it is their own fault, he would have them so.

Secondly, Be not afraid;

1. “Be not afraid of me, now that you know it is I; surely you will not fear, for you know I mean you no hurt.” Note, Christ will not be a terror to those to whom he manifests himself; when they come to understand him aright, the terror will be over.

2. “Be not afraid of the tempest, of the winds and waves, though noisy and very threatening; fear them not, while I am so near you. I am he that concerns himself for you, and will not stand by and see you perish.”
Note, Nothing needs be a terror to those that have Christ near them, and know he is theirs; no, not death itself.

John Calvin

As Christ is not known to be a Deliverer till he actually makes his appearance, he speaks, and desires his disciples to recognise him. That confidence, to which he exhorts them, is represented by him as founded on his presence; plainly implying that, since they perceive him to be present with them, there are abundant grounds of hope. But as terror had already overpowered their minds, he corrects that terror, lest it should hinder or abate their confidence: not that they could all at once lay aside fear and experience unmingled joy, but because it was necessary that the fear which had seized them should be allayed, that it might not destroy their confidence. Although to the reprobate the voice of the Son of God is deadly, and his presence appalling, yet the effect which they produce on believers is here described to us as widely different. They cause inward peace and strong confidence to hold the sway over our hearts, that we may not yield to carnal fears. But the reason why we are disturbed by unfounded and sudden alarms is, that our ingratitude and wickedness prevent us from employing as shields the innumerable gifts of God, which, if they were turned to proper account, would give us all necessary support. Now though Christ appeared at the proper time for rendering assistance, yet the storm did not immediately cease, till the disciples were more fully aroused both to desire and to expect his grace. And this deserves our attention, as conveying the instruction, that there are good reasons why the Lord frequently delays to bestow that deliverance which he has ready at hand.

Matthew 13:16,17

But blessed are your eyes because they see, and your ears because they hear. For truly I tell you, many prophets and righteous people longed to see what you see but did not see it, and to hear what you hear but did not hear it.

Albert Barnes

Blessed are your eyes ... That is, you are happy that you are permitted to see truth which they will not see. You are permitted to understand the spiritual meaning of the parables, and in some degree the plan of salvation.

Many prophets and righteous men ... They wished to see the times of the Messiah. They looked to it as a time when the hopes of the world would be fulfilled and when the righteous would be happy, Abraham rejoiced to see my day ... (Jn 8:56). Compare also 1 Pet 1:10-12, Heb 11:13. So Isaiah and the prophets looked forward to the coming of the Messiah as the consummation of their wishes and the end of the prophecies, Rev 19:10. The object always dearest to the hearts of all righteous people is to witness the coming and advancement of the kingdom of Christ. Cf Rev 22:20.

John Gill

But blessed are your eyes, etc .... Which is to be understood both of corporal and intellectual sight: it was their happiness to see Christ in the flesh and converse with him in person, be eyewitnesses of his majesty and see with their own eyes the miracles ... the proofs and attestations of those doctrines they were to publish to all the world; and it was still their greater happiness, that they saw his glory, as the glory of the only begotten of the Father, full of grace and truth: many saw him in the flesh ... with their bodily eyes, but saw no beauty nor comeliness ... nothing amiable and desirable ... but these saw his personal and transcendent glories, as the Son of God, his fullness as mediator, his suitableness as a Saviour and Redeemer and all the characters of the Messiah in him; and so believed, and were sure that he was the Christ, the Son of the living God: they saw Christ, not in the promise, as Abraham and other patriarchs ...  through types and shadows as the saints of the OT ... to them it was given to know and understand the mysteries of grace, respecting the person, offices, obedience, sufferings and death of Christ.

And your ears, etc. This also must be understood of corporal and intellectual hearing, another branch of their present happiness. They heard the words of truth from the lips of that great prophet Moses said should rise up among them ... whom they should hear ... heard ... a voice from heaven, declaring him to be the beloved Son of God, in whom he was well pleased ... heard the gospel preached by him, not only so as to be affected with it and give their assent to it but also to understand it spiritually and experimentally, and to bring forth the fruit of it; and so were that sort of hearers, signified by the good ground in the parable .... the forms of speech in which the happiness of the disciples is here expressed seem to be in common use with the Jews, when they would extol the peculiar attainments of a man ....

For verily I say etc .... This is added for the further confirmation of what is before said, concerning the happiness of the disciples, in seeing and hearing what they did:
that many prophets, and righteous men Luke (10:24) says "kings"

have desired to see those things which ye see, etc To see Christ in the flesh, and have a clearer insight into the knowledge of the mysteries of grace, were things very desirable to men of the highest class in church and state, and of the best characters, such as Abraham (Jn 8:56) Jacob (Gn 49:18) David (Ps 14:7) ... Isaiah, and the saints with him (25:9) with many others. These indeed had a sight of Christ, but a very distant one; they saw him afar off in the promises and prophecies of him; and not very clearly, but through dark types and cloudy sacrifices; whereas the disciples saw him in person, heard him preach, took in the evidence of his miracles, and felt the power of his doctrines, and spiritually and savingly understood them. ....

Matthew Henry

For the exciting of our thankfulness, and the quickening of our diligence, it is good for us to consider what means we enjoy and what discoveries are made to us, now under the gospel, above what they had, and enjoyed, who lived under the OT dispensation, especially in the revelation of the atonement for sin; see what are the advantages of the NT above the OT ... and see that our improvements be proportionable to our advantages.

Matthew 12:8

For the Son of Man is Lord of the Sabbath.

Albert Barnes

To crown all, Christ says that he was Lord of the Sabbath. He had a right to direct the manner of its observance - undoubted proof that he is divine.

David Brown

In what sense now is the Son of man Lord of the sabbath day? Not surely to abolish it - that surely were a strange lordship, especially just after saying that it was made or instituted for Man - but to own it, to interpret it, to preside over it and to ennoble it, by merging it in the “Lord’s Day” (Rev 1:10), breathing into it an air of liberty and love necessarily unknown before, and thus making it the nearest resemblance to the eternal sabbatism.

Matthew Henry

The Son of man is Lord even of the sabbath day That law, as all the rest, is put into the hand of Christ, to be altered, enforced, or dispensed with, as he sees good. It was by the Son that God made the world, and by him he instituted the sabbath in innocency; by him he gave the ten commandments at mount Sinai, and as Mediator he is entrusted with the institution of ordinances, and to make what changes he thought fit; and particularly, as being Lord of the sabbath, he was authorized to make such an alteration of that day, as that it should become the Lord's day, the Lord Christ's day. And if Christ be the Lord of the sabbath, it is fit the day and all the work of it should be dedicated to him. By virtue of this power Christ here enacts, that works of necessity, if they be really such, and not a pretended and self-created necessity, are lawful on the sabbath day; and this explication of the law plainly shows that it was to be perpetual. Exceptio firmat regulam - The exception confirms the rule.

Thomas Scott

He was Ruler of his church. Thus he intimated, that, as "Son of God" he instituted the Sabbath, gave the law from Sinai, and had lost none of his authority by his humiliation, but should make such alterations respecting the time and circumstances of observing this sacred rest, as it became him. It cannot be that Christ would have so often discussed this subject, and shown what is lawful on the Sabbath, without allowing exceptions, if he had not intended, that the institution substantially should continue in full force under the Christian dispensation.

Philip Doddridge

This certainly implies that the Sabbath was an institution of great and distinguished importance; and may perhaps refer also to that signal authority which Christ, by the ministry of his apostles should exert over it, in changing it from the seventh to the first day of the week.