This passage does not say the Mosaic Law is eternal which is what we are talking about. Keeping the Sabbath, the dietary laws, tithing and the festivals etc that pertain to the Mosaic Law have no place in the Christian way of life. To insist this is how a Christian must live is to become as the Judaizers which Paul roundly condemned.
Psalm 119:160
The entirety of Your word
is truth, And every one of Your righteous judgments
endures forever.
The Hebrew word "mishpatim" refers to laws in regard to righteousness and justice. God's righteousness is eternal (Psalms 119:142), therefore all of His instructions for how to testify about His righteousness and justice are also eternal (Psalms 119:160). Likewise, God's holiness is eternal, therefore all of His instructions for how to testify about HIs holiness are also eternal, and so forth for other aspects of God's nature. In 1 Peter 1:16, we are told to be holy for God is holy, which is a quote from Leviticus where God was giving instructions for how to do that, which includes keeping God's Sabbaths holy (Leviticus 19:2-3) and refraining from eating unclean animals (Leviticus 11:44-45), so by following those eternal instructions we are testifying about God's eternal holiness. Our good works testify about God's eternal goodness, which is why they bring glory to Him (Matthew 5:16) and so forth. It would be contradictory if God's nature were eternal while the way to testify about His nature were not.
Christ set a sinless example for us to follow of how to walk in obedience to the Mosaic Law and we are told to follow his example (1 Peter 2:21-22) and that those who are in Christ are obligated to walk in the same way he walked (1 John 2:6). Being a Christian is about about walking in Christ's example and it is absurd to think that that has no place in the Christian life or to to think that the problem that Paul had with the Judaizers was that they were teaching Gentiles how to follow Christ.
No it is not. The law we are under now is variously called the Law of the Spirit of life in Christ Jesus (Rom.8:2), the Law of Christ (Gal.6:2) or the Law of Love (Gal.5:14). It is
not the Mosaic Law. We do not live by "don't eat this or don't do that", we live by grace through faith in the One who died for us. Christ ends the Law of Moses for it's very purpose was to lead to Christ. This is why Christ is the fulfillment.
Romans 10:4
For Christ
is the end of the law for righteousness to everyone who believes.
John 1:17
For the law was given through Moses,
but grace and truth came through Jesus Christ.
The Spirit is God and the Law of Moses was given by God, so you are giving no basis for thinking that the Law of the Spirit of life in Christ Jesus is not the Law of Moses, especially when Christ spent his ministry teaching us how to obey the Law of Moses by word and by example. The greatest two commandments of the Mosaic Law are to love God and our neighbor, so obeying those commandments is not doing something other than obeying the Law of Moses. In Psalms 119:29-30, he wanted to put false ways far from him, for God to be gracious to him by teaching him to obey the Law of Moses, and he chose the way of faithfulness by setting it before him, so that has always been the one and only way to live by grace through faith in the one who died for us. In Psalms 119:142, the Mosaic Law is truth, so grace and truth came through Jesus because he spent his ministry teaching his followers to obey the Mosaic Law by word and by example. In John 1:16-17, is says grace upon grace, so it is speaking about one example of grace being added on top of another and there is no "but" in Greek in John 1:17.
In Matthew 7:23, Jesus said that he would tell those who are workers of lawlessness to depart from him because he never knew them, so the Mosaic Law leads us to Christ because knowing him through experiencing his nature is the goal of the law. The Mosaic Law does not lead us to Christ so that we can then reject everything that he taught and go back to living in sin. In Matthew 5:17-19, Jesus said that he came to fulfill the Mosaic Law in contrast with saying that he did not come to abolish it and he warned against relaxing the least part of it, so saying that he ended it is calling him a liar and disregarding his warning. Moreover, in Romans 3:31, Paul confided that our faith does not abolish God's law, but rather our faith upholds it, yet you are seeking to abolish it instead of seeking to uphold it through faith. Eternal instructions for how to testify about God's eternal nature can't be abolished without first abolishing God. If you believe in the existence of the God of Israel, whose nature is testified about by the Law of Moses, then you will live in way that testifies about Him by obeying it.
This is not saying the Mosaic Law equips us for every good work. It is talking about the scriptures, the word of God. Christ is the word. It is Christ in whom lies the power to produce good in us, not the law. The law is powerless to make one righteous and good.
2Tim.3:15-17
15 and that from childhood you have known the Holy Scriptures, which are able to make you wise for salvation through faith which is in Christ Jesus. 16 All Scripture
is given by inspiration of God, and
is profitable for doctrine, for reproof, for correction, for instruction in righteousness, 17 that the man of God may be complete, thoroughly equipped for every good work.
Romans 8:3
For what the law was powerless to do because it was weakened by the flesh, God did by sending his own Son in the likeness of sinful flesh to be a sin offering. And so he condemned sin in the flesh,
"All Scriptures" is at the very the very least inclusive of the Mosaic Law if not primarily referring to it. In 2 Timothy 3:15-17, Paul referred to Holy Scriptures that Timothy had available to him from childhood, which could only be referring to OT Scriptures because none of the books of the NT had yet been written at the time of Timothy's childhood. The things that OT Scriptures are profitable for are all in regard to our conduct and the code of conduct in OT Scriptures is the Mosaic Law. So the the Mosaic Law is God's instructions for how to do good works, not for how become good, but rather it is God who makes us good and doing good works in obedience to the Mosaic is what that looks like.
The Mosaic Law is truth (Psalms 119:142), the sum of God's word is truth (Psalms 119:142), God's word became flesh and dwelt among us (John 1:14), and he is truth (John 14:6), so he set a sinless example of how to walk in obedience to the Mosaic. The Mosaic Law is God's word, so the way to be saved through faith in the one who is the embodiment of God's word is by us embodying God's word through following his example.
In Romans 8:3-4, Jesus set us free from sin so that we might be free to obey the Mosaic Law and meet its righteous requirement. In Romana 8:4-7, those who walk in the Spirit are contrasted with those who have minds set on the flesh who are enemies of God who refuse to submit to the Mosaic Law.
It was given to lead you to Christ. Are you in Christ? You have already arrived. You're like a man hoarding bus tickets after he has arrived at his destination. It serves you no purpose now. Now we turn our hearts to grace and truth, learning to walk by means of the Spirit living in accordance with the highest law, the law of love, a law far harder to keep than the Mosaic law.
The Mosaic Law leads us to Christ because it was given for the purpose of teaching us how to know him through experiencing his nature, which is eternal life (John 17:3), and which is why those who are in Christ are obligated to walk in the same way he did (1 John 2:6), which was in obedience to the Mosaic Law. The purpose of the Mosaic Law teaching us how to be in Christ and have a relationship with Christ is so that we will then spent our life growing in a relationship with Him, not so that we will then reject him and go back to doing what it reveals to be sin. God is gracious to us by teaching us to obey the Mosaic Law and the Mosaic Law is truth and is the way to walk in the Spirit, so you are arguing in favor of turning away from that.