Matthew 5:17‭-‬19 The Law

"Do not think that I came to abolish the Law or the Prophets; I did not come to abolish but to fulfill.  For truly I say to you, until heaven and earth pass away, not the smallest letter or stroke shall pass from the Law until all is accomplished.  Whoever then annuls one of the least of these commandments, and teaches others to do the same, shall be called least in the kingdom of heaven; but whoever keeps and teaches them, he shall be called great in the kingdom of heaven. [Matthew 5:17‭-‬19 NASB]

Jesus came to fulfill the Law. Much of the teaching of the New Testament centers around the doctrine that salvation is by grace through faith, apart from the Law. Paul says, "But now apart from the Law the righteousness of God has been manifested, being witnessed by the Law and the Prophets, even the righteousness of God through faith in Jesus Christ for all those who believe; for there is no distinction." [Romans 3:21‭-‬22 NASB]

Even so, he is careful to note that he is not teaching that the Law is abolished. "Do we then nullify the Law through faith? May it never be! On the contrary, we establish the Law. [Romans 3:31 NASB] The Law and Prophets (the Old Testament) are the inspired word of God. The fact that we are not under the Law, but are under grace does not change that. However, our relationship to the Law has been changed.

The Old Testament is a covenant. "Or do you not know, brethren (for I am speaking to those who know the law), that the law has jurisdiction over a person as long as he lives?...Therefore, my brethren, you also were made to die to the Law through the body of Christ, so that you might be joined to another, to Him who was raised from the dead, in order that we might bear fruit for God." [Romans 7:1-4 NASB]

In Christ, we died to the Law, "But now we have been released from the Law, having died to that by which we were bound, so that we serve in newness of the Spirit and not in oldness of the letter." [Romans 7:6 NASB]

The purpose of the Law is to teach us of our sinful nature. "for sin, taking an opportunity through the commandment, deceived me and through it killed me. So then, the Law is holy, and the commandment is holy and righteous and good. Therefore did that which is good become a cause of death for me? May it never be! Rather it was sin, in order that it might be shown to be sin by effecting my death through that which is good, so that through the commandment sin would become utterly sinful." [Romans 7:11-13 NASB]

The problem with the Law, is that it is impossible to keep all of the commands of the Law due to our sinful nature. "For we know that the Law is spiritual, but I am of flesh, sold into bondage to sin. For what I am doing, I do not understand; for I am not practicing what I would like to do, but I am doing the very thing I hate. But if I do the very thing I do not want to do, I agree with the Law, confessing that the Law is good. So now, no longer am I the one doing it, but sin which dwells in me. For I know that nothing good dwells in me, that is, in my flesh; for the willing is present in me, but the doing of the good is not." [Romans 7:14-18 NASB]

But through Jesus, we are no longer under the Law, because through Jesus, the Law is fulfilled in us, "For what the Law could not do, weak as it was through the flesh, God did: sending His own Son in the likeness of sinful flesh and as an offering for sin, He condemned sin in the flesh, so that the requirement of the Law might be fulfilled in us, who do not walk according to the flesh but according to the Spirit." [Romans 8:3-4 NASB]

In terms of our salvation the Old Covenant is obsolete. But it is not irrelevant. It is still the word of God. Learn from the Old covenant without becoming bound by it, because we are under a New Covenant through Christ.

But now He has obtained a more excellent ministry, by as much as He is also the mediator of a better covenant, which has been enacted on better promises. For if that first covenant had been faultless, there would have been no occasion sought for a second.... "For this is the covenant that I will make with the house of Israel after those days, says the Lord: I will put  my laws into their minds, and I will write them on their hearts. And I will be their God, and they shall be my people." [Hebrews 8:6‭-‬10‭ NASB]