Matthew 5:17-20 "Do not think that I came to destroy the Law or the Prophets. I did not come to destroy but to fulfill. For assuredly, I say to you, till heaven and earth pass away, one jot or one tittle will by no means pass from the law till all is fulfilled. Whoever therefore breaks one of the least of these commandments, and teaches men so, shall be called least in the kingdom of heaven; but whoever does and teaches them, he shall be called great in the kingdom of heaven. For I say to you, that unless your righteousness exceeds the righteousness of the scribes and Pharisees, you will by no means enter the kingdom of heaven."
Commentary: "The relation between our Lord's teaching and that of the Old Testament, is cleared up by our Lord in one striking sentence. He says, "Don't think that I came to destroy the law, or the prophets. I didn't come to destroy, but to fulfill." These are remarkable words. They were deeply important when spoken, as satisfying the natural anxiety of the Jews on the point. They will be deeply important as long as the world stands, as a testimony that the religion of the Old and New Testament is one harmonious whole.
The Lord Jesus came to fulfill the predictions of the prophets, who had long foretold that a Savior would one day appear. He came to fulfill the ceremonial law, by becoming the great sacrifice for sin, to which all the Mosaic offerings had ever pointed. He came to fulfill the moral law, by yielding to it a perfect obedience, which we could never have yielded--and by paying the penalty for our breach of it with His atoning blood, which we could never have paid. In all these ways He exalted the law of God, and made its importance more evident even than it had been before. In a word, "He magnified the law and made it honorable." (Isaiah 42:21.)
There are deep lessons of wisdom to be learned from these words of our Lord. Let us consider them well, and lay them up in our hearts.
Let us beware of despising the Old Testament under any pretense whatever. Let us never listen to those who bid us throw it aside as an obsolete, antiquated, useless book. The religion of the Old Testament is the embryo of Christianity. The Old Testament is the Gospel in the bud. The New Testament is the Gospel in full flower. The Old Testament is the Gospel in the blade. The New Testament is the Gospel in full ear. The saints in the Old Testament saw many things through a glass darkly. But they all looked by faith to the same Savior, and were led by the same Spirit as ourselves. These are no light matters. Much infidelity begins with an ignorant contempt of the Old Testament.
Let us, for another thing, beware of despising the law of the Ten Commandments. Let us not suppose for a moment that it is set aside by the Gospel, or that Christians have nothing to do with it. The coming of Christ did not alter the position of the Ten Commandments one hair's breadth. If anything, it exalted and raised their authority. (Rom. 3:31.) The law of the Ten Commandments is God's eternal measure of right and wrong. By it, is the knowledge of sin. By it, the Spirit shows men their need of Christ, and drives them to Him. To it, Christ refers His people as their rule and guide for holy living. In its right place it is just as important as "the glorious Gospel." It cannot save us. We cannot be justified by it. But never, never let us despise it. It is a symptom of an ignorant and unhealthy state of religion, when the law is lightly esteemed. The true Christian "delights in God's law." (Rom. 7:22.)
In the last place, let us beware of supposing that the Gospel has lowered the standard of personal holiness, and that the Christian is not intended to be as strict and particular about his daily life as the Jew. This is an immense mistake, but one that is unhappily very common. So far from this being the case, the sanctification of the New Testament saint ought to exceed that of him who has nothing but the Old Testament for his guide. The more light we have, the more we ought to love God. The more clearly we see our own complete and full forgiveness in Christ, the more heartily ought we to work for His glory. We know what it cost to redeem us far better than the Old Testament saints did. We have read what happened in Gethsemane and on Calvary, and they only saw it dimly and indistinctly as a thing yet to come. May we never forget our obligations! The Christian who is content with a low standard of personal holiness has got much to learn." - JC RYLE