Jesus said, “Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them. For truly I tell you, until heaven and earth disappear, not the smallest letter, not the least stroke of a pen, will by any means disappear from the Law until everything is accomplished” (Matthew 5:17–18). This important statement of our Lord gives us insight into His mission and the character of God’s Word.
Jesus’ declaration that He came to fulfill the Law and the Prophets, not to abolish them, obviously contains two statements in one. There is something Jesus did and something He did not do. At the same time, Jesus emphasized the eternal nature of the Word of God.
Jesus goes out of His way to promote the authority of the Law of God. He did not come to abolish the Law, regardless of what the Pharisees accused Him of. In fact, Jesus continues His statement with a commendation for those who teach the Law accurately and hold it in reverence: “Therefore anyone who sets aside one of the least of these commands and teaches others accordingly will be called least in the kingdom of heaven, but whoever practices and teaches these commands will be called great in the kingdom of heaven” (Matthew 5:19).
Note the qualities that Jesus attributes to the Word of God, referenced as “the Law and the Prophets”: 1) The Word is everlasting; it will outlast the natural world. 2) The Word was written with intent; it was meant to be fulfilled. 3) The Word possesses plenary authority; even the smallest letter of it is established. 4) The Word is faithful and trustworthy; “everything” it says will be accomplished. No one hearing Jesus’ words in the Sermon on the Mount could doubt His commitment to the Scriptures.
Consider what Jesus did not do in His ministry. In Matthew 5:17, Jesus says that He did not come to abolish the Law and the Prophets. In other words, Jesus’ purpose was not to abrogate the Word, dissolve it, or render it invalid. The Prophets will be fulfilled; the Law will continue to accomplish the purpose for which it was given (see Isaiah 55:10–11).
Next, consider what Jesus did do. Jesus says that He came to fulfill the Law and the Prophets. In other words, Jesus’ purpose was to establish the Word, to embody it, and to fully accomplish all that was written. “Christ is the culmination of the law” (Romans 10:4). The predictions of the Prophets concerning the Messiah would be realized in Jesus; the holy standard of the Law would be perfectly upheld by Christ, the strict requirements personally obeyed, and the ceremonial observances finally and fully satisfied.
Jesus Christ fulfilled the Prophets in that, in His first coming alone, He fulfilled hundreds of prophecies concerning Himself (e.g., Matthew 1:22; 13:35; John 19:36; Luke 24:44). Jesus Christ fulfilled the Law in at least two ways: as a teacher and as a doer. He taught people to obey the Law (Matthew 22:35–40; Mark 1:44), and He obeyed the Law Himself (John 8:46; 1 Peter 2:22). In living a perfect life, Jesus fulfilled the moral laws; in His sacrificial death, Jesus fulfilled the ceremonial laws. Christ came not to destroy the old religious system but to build upon it; He came to finish the Old Covenant and establish the New.
Jesus came not to destroy the Law and the Prophets but to fulfill them. In fact, the ceremonies, sacrifices, and other elements of the Old Covenant were “only a shadow of the good things that are coming—not the realities themselves” (Hebrews 10:1). The tabernacle and temple were “holy places made with hands,” but they were never meant to be permanent; they were but “copies of the true things” (Hebrews 9:24, ESV). The Law had a built-in expiration date, being filled as it was with “external regulations applying until the time of the new order” (Hebrews 9:10).
In His fulfillment of the Law and Prophets, Jesus obtained our eternal salvation. No more were priests required to offer sacrifices and enter the holy place (Hebrews 10:8–14). Jesus has done that for us, once and for all. By grace through faith, we are made right with God: “He forgave us all our sins, having canceled the charge of our legal indebtedness, which stood against us and condemned us; he has taken it away, nailing it to the cross” (Colossians 2:14).
There are some who argue that, since Jesus did not “abolish” the Law, then the Law is still in effect—and still binding on New Testament Christians. But Paul is clear that the believer in Christ is no longer under the Law: “We were held in custody under the Law, locked up until faith should be revealed. So the Law became our guardian to lead us to Christ, that we might be justified by faith. Now that faith has come, we are no longer under a guardian” (Galatians 3:23–25, BSB). We are not under the Mosaic Law but under “the law of Christ” (see Galatians 6:2).
If the Law is still binding on us today, then it has not yet accomplished its purpose—it has not yet been fulfilled. If the Law, as a legal system, is still binding on us today, then Jesus was wrong in claiming to fulfill it and His sacrifice on the cross was insufficient to save. Thank God, Jesus fulfilled the whole Law and now grants us His righteousness as a free gift. “Know that a person is not justified by the works of the law, but by faith in Jesus Christ. So we, too, have put our faith in Christ Jesus that we may be justified by faith in Christ and not by the works of the law, because by the works of the law no one will be justified” (Galatians 2:16).
https://www.gotquestions.org/abolish-fulfill-law.html