Romans 3: 31, “Do we nullify the Law through faith? God forbid! On the contrary, we establish the Law.” (NASB)
Jesus is the subject of the Law and meets the demands of the Law. The law was the tutor that showed us that we needed a Saviour, Galatians 3: 24- 25. The Brazen Altar of the Tabernacle, the Table of Shewbread, the Lamp Stand, and the Ark of the Covenant all pointed directly to the Lord Jesus. Matthew 5: 17- 20, Jesus told the Pharisees that He came to fulfill the Law not abolish it.
No, though we do say that the Law will not justify us, yet we do not therefore say that it was given in vain, or is of no use; no, we establish the right use of the Law, and secure its standing, by fixing it on the right basis. The Law is still of use to convince us of what is past, and to direct us for the future; though we cannot be saved by it as a covenant, yet we own it, and submit to it, as a rule in the Hand of the Mediator, subordinate to the Law of Grace; and so are so far from overthrowing that we establish the Law. (Henry)
The Law was given to show us that we need a Saviour, seeing that we are under-develop, unequipped and horribly unable to save ourselves. This is why the Jesus’ death on Calvary in called the Finished Work of the Cross, He did it all. All we have to do is exhibit child like faith.
The Lord Jesus completed the Law by living up to the strictness and bondage of it, Galatians 4: 4, 6. This is how we established the Law by exhibiting faith in Christ and Him Crucified. This is the only way a Just and Righteous God can justify sinful mankind and still be Just and Right. He laid down a plan, and we follow that plan. In the Person of the Lord Jesus Christ as our Sin Offering, our Passover Lamb, as our Sin Substitution He stood in front of the Wrath of God and took the full brute of God‘s Holy and Righteous Judgment. This is why it is called Grace; God’s Riches At Christ Expense.