Regarding the utility of the Law of Moses in the life of a believer in Christ:
Before Jesus’ resurrection He said…
Matthew 5:17 – “Do not think that I came to destroy the Law or the Prophets. I did not come to destroy but to fulfill.”
After His resurrection He said…
44 …“These are the words which I spoke to you while I was still with you, that all things must be fulfilled which were written in the Law of Moses and the Prophets and the Psalms concerning Me.”
45 And He opened their understanding, that they might comprehend the Scriptures.
46 Then He said to them, “Thus it is written, and thus it was necessary for the Christ to suffer and to rise from the dead the third day
Which leads Paul to say…
Romans 10:4 – For Christ is the end [fulfillment] of the law for righteousness to everyone who believes.
Romans 6:14 – For sin shall not have dominion over you, for you are not under law but under grace [a word closer in meaning to “power” than “mercy”].
Galatians 5:18 – But if you are led by the Spirit, you are not under the law.
2 For the law of the Spirit of life in Christ Jesus has made me free from the law of sin and death.
3 For what the law could not do in that it was weak through the flesh, God did by sending His own Son in the likeness of sinful flesh, on account of sin: He condemned sin in the flesh,
4 that the righteous requirement of the law might be fulfilled in us who do not walk according to the flesh but according to the Spirit.
Romans 7:6 – But now we have been delivered from the law, having died to what we were held by, so that we should serve in the newness of the Spirit and not in the oldness of the letter.
1 Timothy 1:
8 But we know that the law is good if one uses it lawfully,
9 knowing this: that the law is not made for a righteous person, but for the lawless and insubordinate, for the ungodly and for sinners, for the unholy and profane, for murderers of fathers and murderers of mothers, for manslayers,
10 for fornicators, for sodomites, for kidnappers, for liars, for perjurers, and if there is any other thing that is contrary to sound doctrine,
11 according to the glorious gospel of the blessed God which was committed to my trust.
Believers in Christ follow the Holy Spirit’s dynamic interpretation of the scriptures, which will match Jesus’ focus on the true purposes of the law. Examples include: “Sabbath is for man”, hatred = murder, lust = adultery, loving “neighbors” means enemies too, mercy > sacrifice, the widow’s mite > rich man’s fortune, etc.
The Word of God, as spoken by the Holy Spirit, imparts life (Matthew 4:4; John 6:68; 2 Corinthians 3:6).
For people who aren’t led by the Spirit, the letter of the law serves as a moral boundary, but it cannot save them.
NOTE: All verses are from the New King James Version; brackets are mine