“Those to whom Christ preached, and for whose use he gave these instructions to his disciples, were such as in their religion had an eye, 1. To the scriptures of the Old Testament as their rule, and therein Christ here shows them they were in the right: 2. To the scribes and the Pharisees as their example, and therein Christ here shows them they were in the wrong; for,
I. The rule which Christ came to establish exactly agreed with the scriptures of the Old Testament, here called the law and the prophets. The prophets were commentators upon the law, and both together made up that rule of faith and practice which Christ found upon the throne in the Jewish church, and here he keeps it on the throne.
1. He protests against the thought of cancelling and weakening the Old Testament; Think not that I am come to destroy the law and the prophets. (1.) “Let not the pious Jews, who have an affection for the law and the prophets, fear that I come to destroy them.” Let them be not prejudiced against Christ and his doctrine, from a jealousy that this kingdom he came to set up, would derogate from the honour of the scriptures, which they had embraced as coming from God, and of which they had experienced the power and purity; no, let them be satisfied that Christ has no ill design upon the law and the prophets. “Let not the profane Jews, who have a disaffection to the law and the prophets, and are weary of that yoke, hope that I am come to destroy them.” Let not carnal libertines imagine that the Messiah is come to discharge them from the obligation of divine precepts and yet to secure to them divine promises, to make the happy and yet to give them leave to live as they list. Christ commands nothing now which was forbidden either by the law of nature or the moral law, nor forbids any thing which those laws had enjoined; it is a great mistake to think he does, and he here takes care to rectify the mistake; I am not come to destroy. The Saviour of souls is the destroyer of nothing but the works of the devil, of nothing that comes from God, much less of those excellent dictates which we have from Moses and the prophets. No, he came to fulfil them. That is,

[1.] To obey the commands of the law, for he was made under the law, Gal_4:4. He in all respects yielded obedience to the law, honoured his parents, sanctified the sabbath, prayed, gave alms, and did that which never any one else did, obeyed perfectly, and never broke the law in any thing. [2.] To make good the promises of the law, and the predictions of the prophets, which did all bear witness to him. The covenant of grace is, for substance, the same now that it was then, and Christ the Mediator of it. [3.] To answer the types of the law; thus (as bishop Tillotson expresses it), he did not make void, but make good, the ceremonial law, and manifested himself to be the Substance of all those shadows. [4.] To fill up the defects of it, and so to complete and perfect it. Thus the word plērōsai properly signifies. If we consider the law as a vessel that had some water in it before, he did not come to pour out the water, but to fill the vessel up to the brim; or, as a picture that is first rough-drawn, displays some outlines only of the piece intended, which are afterwards filled up; so Christ made an improvement of the law and the prophets by his additions and explications. [5.] To carry on the same design; the Christian institutes are so far from thwarting and contradicting that which was the main design of the Jewish religion, that they promote it to the highest degree. The gospel is the time of reformation (Heb_9:10), not the repeal of the law, but the amendment of it, and, consequently, its establishment.
2. He asserts the perpetuity of it; that not only he designed not the abrogation of it, but that it never should be abrogated (Mat_5:18); “Verily I say unto you, I, the Amen, the faithful Witness, solemnly declare it, that till heaven and earth pass, when time shall be no more, and the unchangeable state of recompences shall supersede all laws, one jot, or one tittle, the least and most minute circumstance, shall in no wise pass from the law till all be fulfilled;” for what is it that God is doing in all the operations both of providence and grace, but fulfilling the scripture? Heaven and earth shall come together, and all the fulness thereof be wrapped up in ruin and confusion, rather than any word of God shall fall to the ground, or be in vain. The word of the Lord endures for ever, both that of the law, and that of the gospel. Observe, The care of God concerning his law extends itself even to those things that seem to be of least account in it, the iotas and the tittles; for whatever belongs to God, and bears his stamp, be it ever so little, shall be preserved. The laws of men are conscious to themselves of so much imperfection, that they allow it for a maxim, Apices juris non sunt jura – The extreme points of the law are not the law, but God will stand by and maintain every iota and every tittle of his law.
3. He gives it in charge to his disciples, carefully to preserve the law, and shows them the danger of the neglect and contempt of it (Mat_5:19); Whosoever therefore shall break one of the least commandments of the law of Moses, much more any of the greater, as the Pharisees did, who neglected the weightier matters of the law, and shall teach men so as they did, who made void the commandment of God with their traditions (Mat_15:3), he shall be called the least in the kingdom of heaven. Though the Pharisees be cried up for such teachers as should be, they shall not be employed as teachers in Christ’s kingdom; but whosoever shall do and teach them, as Christ’s disciples would, and thereby prove themselves better friends to the Old Testament than the Pharisees were, they, though despised by men, shall be called great in the kingdom of heaven. Note, (1.) Among the commands of God there are some less than others; none absolutely little, but comparatively so. The Jews reckon the least of the commandments of the law to be that of the bird’s nest (Deu_22:6, Deu_22:7); yet even that had a significance and an intention very great and considerable. (2.) It is a dangerous thing, in doctrine or practice, to disannul the least of God’s commands; to break them, that is, to go about either to contract the extent, or weaken the obligation of them; whoever does so, will find it is at his peril. Thus to vacate any of the ten commandments, is too bold a stroke for the jealous God to pass by. it is something more than transgressing the law, it is making void the law, Psa_119:126. (3.) That the further such corruptions as they spread, the worse they are. It is impudence enough to break the command, but is a greater degree of it to teach men so. This plainly refers to those who at this time sat in Moses’ seat, and by their comments corrupted and perverted the text. Opinions that tend to the destruction of serious godliness and the vitals of religion, by corrupt glosses on the scripture, are bad when they are held, but worse when they are propagated and taught, as the word of God. He that does so, shall be called least in the kingdom of heaven, in the kingdom of glory; he shall never come thither, but be eternally excluded; or, rather, in the kingdom of the gospel-church. He is so far from deserving the dignity of a teacher in it, that he shall not so much as be accounted a member of it. The prophet that teaches these lies shall be the tail in that kingdom (Isa_9:15); when truth shall appear in its own evidence, such corrupt teachers, though cried up as the Pharisees, shall be of no account with the wise and good. Nothing makes ministers more contemptible and base than corrupting the law, Mal_2:8, Mal_2:11. Those who extenuate and encourage sin, and discountenance and put contempt upon strictness in religion and serious devotion, are the dregs of the church. But, on the other hand, Those are truly honourable, and of great account in the church of Christ, who lay out themselves by their life and doctrine to promote the purity and strictness of practical religion; who both do and teach that which is good; for those who do not as they teach, pull down with one hand what they build up with the other, and give themselves the lie, and tempt men to think that all religion is a delusion; but those who speak from experience, who live up to what they preach, are truly great; they honour God, and God will honour them (1Sa_2:30), and hereafter they shall shine as the stars in the kingdom of our Father.” Matthew Henry

Excerpt from Matthew Henry Commentaries – Matthew