Did you not understand that the old testament has been done away with and a New Testament has been established by Jesus Christ Himself???
Hebrews 10:9
Then said he, Lo, I come to do thy will, O God. He taketh away the first, that he may establish the second.
(God said He would make a New Covenant - see Jeremiah 31:31-34)
Hebrews 8:6
But now hath Jesus obtained a more excellent ministry, by how much also Jesus is the mediator of a better covenant, which was established upon better promises.
A new covenant does not nullify the promises of a covenant that has already been ratified, so God's covenants are cumulative. The Mosaic Covenant is eternal (Exodus 31:14-17, Leviticus 24:8), so the only way that it can be replaced by the New Covenant is if it cumulative with the Mosaic Covenant, which is what it means to make something obsolete (Hebrews 8:13). So the New Covenant still involves following the Torah (Hebrews 8:10) plus it is based on better promises and has a superior mediator (Hebrews 8:6). The fault that God found with the Mosaic Covenant was not with His law, but with the people for not continuing in their covenant (Hebrews 8:7-9), so the solution to the problem was not for God to do away with His Torah, but to do away with what was hindering us from obeying it. This is why the New Covenant involves God sending His Son to free us from sin so that we might be free to meet the righteous requirement of the Torah (Romans 8:3-4), God taking away our hearts of stone, giving us hearts of flesh, and sending His Spirit to lead us in obedience to the Torah (Ezekiel 36:26-27), and God putting the Torah in our minds and writing it on our hearts (Jeremiah 31:33).
The New Covenant is still made with the same God with the same eternal character traits and therefore the same eternal instructions for how to be a doer of His character traits. For example, the way to be a doer of God's righteousness is straightforwardly based on God's righteousness, not on a particular covenant, and God's righteousness is eternal (Psalms 119:142), therefore all of His instructions for how to be a doer of His righteousness are also eternal (Psalms 119:160). Holiness, righteousness, goodness, justice, mercy, faithfulness, love, joy, peace, patience, kindness, gentleness, self-control, and so forth are all the same, so there is not a different way to be a doer of them under the New Covenant.
God’s people are no longer living under the Law of Moses. Now God’s people are living under the Law of Christ (also called the law of liberty, law of the spirit of life in Christ Jesus – see Galatians 6:2, 1 Corinthians 9:21, James 2:12, James 1:25, Romans 8:2)
In Matthew 4:15-23, Christ began his ministry with the Gospel message to repent for the Kingdom of God is at hand, which was a light to the Gentiles, and the Torah was how his audience knew what sin is (Romans 3:20), so repenting from our disobedience to it is a central part of the Gospel of the Kingdom. Christ also set a sinless example for us to follow of how to walk in obedience to the Torah and as his followers 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). So Christ spent his ministry teaching his followers to obey the Torah by word and by example and I don't see a good reason to think that the Law of Christ is something other than or contrary to anything that Christ taught.
In 1 Corinthians 9:21, Paul used a parallel statement to equate the Law of God with the Law of Christ and the Torah is the Law of God. The Torah is perfect (Psalms 19:7), it is of liberty (Psalms 119:45), and it blesses those who obey it (Psalms 119:1-3), so James 1:25 wasn't saying anything about the Torah that wasn't already said in the Psalms.
Those following the old covenant have returned to the Law of Moses and have fallen from grace
Galatians 5:4
Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace.
I have not suggested that we should follow the Mosaic Covenant, but rather I have been speaking about the way to live under the New Covenant. All throughout the Bible, God wanted His people to repent and to return to obedience to the Torah, and even Christ because his ministry with that Gospel message, so it would be absurd to interpret Galatians 5:4 as Paul warning that we will be cut off from Christ if we repent and believe the Gospel of Christ. 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 Torah, and he chose the way of faith by setting it before him, so this has always been the one and only way of salvation by grace through faith and it would again be absurd to interpret this as him wanting God to be gracious to him by teaching him how to fall from grace, so you are not correctly identifying what Paul was speaking against in Galatians. In Deuteronomy 13, the way that God instruction his children to determine that someone is a false prophet who is not speaking for Him is if they teach against obeying the Torah, so if you agree with me that Paul was a servant of God, then you should be opposed to you interpreting him in a way that makes him out to be a false prophet.