Why would we have to walk in obedience to the law when the Gentiles who were saved in Acts 10 were exempted from keeping the Law? They were only given a few ordnances to obey....................[Acts 15:5 KJV] "But there rose up certain of the sect of the Pharisees which believed, saying, That it was needful to circumcise them, and to command [them] to keep the law of Moses."
[Acts 15:28 KJV] "For it seemed good to the Holy Ghost, and to us, to lay upon you no greater burden than these necessary things;"
[Acts 15:29 KJV] "That ye abstain from meats offered to idols, and from blood, and from things strangled, and from fornication: from which if ye keep yourselves, ye shall do well. Fare ye well."
In Acts 15, the topic that they were discussing is not whether followers of Christ should follow what he taught, but whether salvation is by grace (Acts 15:11) or by circumcision (Acts 15:1). 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 Law of Moses 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 message, which is the. Gospel that Peter argued in Acts 15:6-7 that Gentiles had heard and believed, so he was siding the Pharisees from among the believers in Acts 15:5. In Ezekiel 36:26-27, God will take away our hearts of stone, give us hearts of flesh, and send His Spirit to lead us in obedience to the Law of Moses, which is in accordance with Acts 15:8-9 where Peter argued that Gentiles had received the Spirit and had their hearts cleansed, so again he was siding with the Pharisees from among the believers and the Gentiles in Acts 10 were not exempt from keeping it. In Psalm 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 faith by setting it before him, so this has always been the one and only way of salvation by grace through faith, which is in accordance with what Peter argued in Acts 15:10-11 that Gentiles are saved by grace just as we are, which again is siding with the Pharisees. This means that the heavy burden that no one could bear was not the Law of Moses, but an alternative to salvation by grace, namely salvation by circumcision that was proposed by the men from Judea in Acts 15:1.
Either Acts 15:19-21 contains an exhaustive list for mature believers or it does not, so it would be contradictory to treat it as being an exhaustive list in order to limit which laws Gentiles should follow while also treating it as being an non-exhaustive list by taking the position that there are obviously other laws that Gentiles should follow.
Jesus and the Apostles quoted from the OT hundreds of times in order to support what they were saying, so it doesn't work to take the position that we should only follow what they said but not what they considered to be an authoritative source. Again, Jesus said that man shall not live by bread alone but by every word that comes from the mouth of God and the bottom line is that we must obey God rather than man, so if think that the Jerusalem Council spoke against living by every word that comes from the mouth of God, then you should follow every word that comes from the mouth of God rather than the Jerusalem Council. In Deuteronomy 13, the way that God instructed to determine that someone is a false prophet who is not speaking for Him is if they speak against obeying what He has commanded, so it is either incorrect to interpret the Jerusalem Council as doing that or they were false prophets, but either way followers of Christ should follow his example of obedience to what God has commanded. If you think Acts 15 should be interpreted as ruling against Gentiles following what God has commanded, then you should be opposed considering the Jerusalem Council to be servants of God, and if you think that the Jerusalem Council were servants of God, then you should be opposed to interpreting them as speaking against following what God has commanded, but Deuteronomy 13 does not leave room for you to consider the Jerusalem Council to be servants of God while also thinking that they should be interpreted as speaking against obeying what He has commanded.