According to Romans 9:6-8, Israel is made up of people who are inheritors of the promise, so if you are an inheritor of the promise through faith in Messiah, then you are Israel, and the law is your property. Ephesians 2:19 says a similar thing that Gentiles are made fellow citizens of Israel through faith in Messiah.
We must obey God rather than man, so if God says to do something and man says that you don't have to do that, then we should obey God and disregard what man said. According to Deuteronomy 4:2, no one was given the authority to add to or subtract from God's law and it was a sin to do so, so neither Paul nor the Jerusalem Council had any authority to subtract all but four laws for Gentiles, and neither did they attempt to do so. Furthermore, if you still think Paul did tell anyone not to obey God's law, then according to Deuteronomy 13:4-6, he was a false prophet who was not speaking for God, so you should disregard what he said.
Obeying God's law is about identifying with God, not about identifying with the Jews or their man-made customs. Many Jews incorrectly thought they had a leg up on salvation because they had been circumcised and "all Israel will be saved", but Paul was saying that we are all of equal footing when it comes to being in Christ. He was not denying that there were Jews, Gentiles, slaves, free, men, or women. Furthermore, according to Romans 3:31, our faith in Messiah upholds the law, so and he certainly was not saying our faith in Messiah makes the law unprofitable. Our salvation is from sin (Matthew 1:21) and sin is defined as the transgression of the law (1 John 3:4), so our salvation is from transgressing God's law for the purpose of becoming obedient slaves to Him (Romans 6:16).