I'm using the obsolete idiom because Christians are NOT under the Law and Gentiles are not Jews who are under the Law and in Christ there is no Jew OR Gentile they are seen as the same. This statement Paul made and it wasn't with a little * at the bottom that says "under the Law" either. Let's face it nowhere do we see Paul or any Jewish apostle nor Jesus commanding Gentiles to keep the Law of Moses. One has to IGNORE screaming to the top of their voice the Council of Jerusalem who banned the Law of Moses upon Gentiles. As long as Gentiles are NOT required to keep the Law and ARE saved and Jews and Gentiles are EQUAL in Christ then the Law is obsolete for the Jews to keep because it does NOTHING for them regarding righteousness.
God is holy, righteous, and good, and His law is holy, righteous, and good (Romans 7:12) because it is based off of His character and it is His instructions for how to act in accordance with His character and how to avoid sin. Though it was given to Jews, it is not instructions for how to identify with Jews, but how to identify with God, and it is about the conduct that God wants His chosen people to have. It is the conduct that Christ modeled for us, and as his followers we are to follow in his example (1 Peter 2:21) and walk as he walked (1 John 2:4-6), as go through the process of sanctification and are made to be more like Christ in his character and obedience to the Father. As part of God's chosen people, a holy nation, a royal priesthood, and a treasure of God's own possession (1 Peter 2:9-10), we are to act according to His character and both Jews and Gentiles are told to have a holy, righteous, and good conduct (1 John 3:10, 1 Peter 1:14-16) and to avoid a sinful or lawless conduct (1 John 3:4-10).
Christ was not in disagreement with the Father about which laws should be obeyed or the character that we should have, but rather he said that his teaching was not his own, but that of the one who sent him (John 7:16) and that he came only to do the Father's will (John 6:38), so the law of Christ precisely is the way that he taught how to correctly keep the law of Moses, such as in Matthew 5. However, I would completely agree with you that we are not under the law, but I would disagree that Paul used that phrase to mean that we don't need to obey God because disobeying His law is defined as sin (1 John 3:4) and being under grace doesn't mean we are to sin (Romans 6:15). Rather Paul specified that we died to that which held us captive (Roman 7:6), so we are not under the law in the sense that it no longer has power over us to condemn us to death for breaking it, which is the point he is building to (Roman 8:1). However, all throughout the Bible God wanted obedience from us, so He has no reason to free us from obeying Him, nor should we even want to be free from what is holy, righteous, and good. We were freed from sin and disobedience to God's law so that we could be free to have a righteous conduct in obedience to Him (Romans 6:15-19), not so that we could be free to continue in disobedience.
The Jerusalem Council never ruled that Gentiles were not to have a holy, righteous, and good conduct, nor did they have the authority to countermand God. We must always obey God rather than men, and if you ever interpret the Bible as saying that we should obey men rather than God, such as obeying the Jerusalem Council rather than God, then you have misinterpreted the Bible.
Simply put.....
Galatians 5:18New American Standard Bible (NASB)
18 But if you are led by the Spirit, you are not under the Law.
If you want to be under the Law then you are probably kicking the Holy Spirit to the curb in your effort to be righteous.
Indeed, if you are led by the Spirit that you are above the law in that the Spirit will lead you in a higher observance of the law that exceeds it's written requirements. Walking by faith in the Spirit is the right way that we are to obey God, while trying to obey God through our own effort without the Spirit leads to death.
1 Corinthians 9:20-22New American Standard Bible (NASB)
20 To the Jews I became as a Jew, so that I might win Jews; to those who are under the Law, as under the Law though not being myself under the Law, so that I might win those who are under the Law; 21 to those who are without law, as without law,
though not being without the law of God but under the law of Christ, so that I might win those who are without law. 22 To the weak I became weak, that I might win the weak; I have become all things to all men, so that I may by all means save some.
And here Paul admits to NOT being under the Law.
Indeed, Paul said that he wasn't under the law, but note that he also said that he was not without the law of God, but under the law of Christ, which are parallel statements saying the same thing.
2 Peter 3:14-17 And count the patience of our Lord as salvation, just as our beloved brother Paul also wrote to you according to the wisdom given him, 16 as he does in all his letters when he speaks in them of these matters. There are some things in them that are hard to understand, which the ignorant and unstable twist to their own destruction, as they do the other Scriptures. 17 You therefore, beloved, knowing this beforehand, take care that you are not carried away with the error of lawless people and lose your own stability.
In other words, Paul is difficult to understand, but those who are ignorant and unstable will twist his words and fall into the error of lawlessness. This is saying that if you interpret Paul as being in favor of lawlessness and against obedience God, then you are wrong.