Romans 2:14
When Gentiles, who do not possess the law, do instinctively what the law requires, these, though not having the law, are a law to themselves.
Law (Mosaic) belongs to the Mosaic Covenant applied only to the Jews.
Romans 2:13-16 saying that only the doers of the Mosaic Law will be justified, that Gentile believers are by nature doers of it, and they show that it is written on their hearts is the opposite of saying that it applies only to the Jews.
Though except for Sabbath, the other 10 commandments are mentioned by Jesus and are part of the New Covenant.
Jesus quoted Deuteronomy three times in order to defeat the temptations of Satan, which included saying that man shall not live by bread alone but by every word that comes from the mouth of God (Deuteronomy 8:3, so he affirmed he affirmed God as being an authoritative source and we have no need for him to have specifically repeated everything that God has spoken in order to know that we should still obey God, which includes obeying what God spoke in Deuteronomy 5:12-15 in regard to keeping the Sabbath holy.
Jesus also set a sinless example for us to follow of how to walk in obedience to the Mosaic Law, so he would have still taught full obedience to it by example even if he hadn't repeated any laws, including keeping the Sabbath holy, 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 that he walked (1 John 2:6). So Christ spent his ministry teaching his followers to obey the Mosaic Law by word and by example and the reason why he established the New Covenant was not in order to nullify anything that he spent his ministry teaching or so that we could continue to have the same lawlessness that caused the New Covenant to be needed in the first place, but rather the New Covenant still involves following the Mosaic Law (Jeremiah 31:33).
Commendments in OT serve as laws, while in the New Covenant they are teachings and commands from Jesus, in case you breakt them you given the chance to repent sincerely. Laws leave no room for repentance, you break them you are done.
The Mosaic Law came with instructions for what to do when people sinned, the prophets consistently called the Israelites to repent and return to obedience to it, and even Jesus began his ministry with that Gospel message (Matthew 4:15-23), so it was not presented as something that left no room for repentance.
Law (Mosaic) is for God to illustrate, through His own chosen people, what God's heavenly Law (applicable to angels and humans alike) could mean such that humans can have a grasp on what God's Grace could mean. Earth is an environment where you can't abide Law to survive, and faith remains the only way out. That's what the New Covenant is for. It means we would try our best to abide by, while the Covenant would save us from where failed. Law to the gentiles is,
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 Mosaic Law, 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 faith is not an alternative way out. We embody what we believe about God through our works, such as with James 2:18 saying that he would show his faith through his works, so faith is about having the right motivation for our works, not about doing something else instead. In Revelation 14:12, those who kept faith in Jesus are the same as those who kept God's commandments.
