When Paul wrote to the Galatians, he was addressing a specific problem: the Galatians had come to believe that they were to believe in Christ AND follow the Old Testament Law. He clearly explained that faith in Christ was separate from OT Law and freed us from its requirements. We are made righteous in God's sight not by following the OT Law but by faith.
Paul gave the church many instructions. If we take your approach, we conclude that Paul's "laws" are merely additions to Moses' Law. They aren't. The Law (as Paul used the term) was the OT law only... circumcision, temple offerings, feasts, etc.
In one sense, law is law, yes, but God didn't give the command "don't wear clothing made from two types of thread" to Christians; He gave it to Israelites, and Christians are not bound by it.
When we conflate all of the NT instructions with the OT law, we get a mishmash of confusing and incompatible requirements which lead to all manner of sects holding to this bit but not that bit. "Rightly dividing the Word" means (at least) understanding which parts are applicable to us as Christians... and which aren't.
The explanations that Jesus gave in the "sermon on the mount" show how the OT law is to be applied: not with rigorous following of the letter, but with the heart. The Holy Spirit within the believer guides and convicts us to love God and our neighbour... not by careful following of written commands, but with love.
I still don't understand. Jesus' command to seek foremost the kingdom of GOD and his righteousness was just as much law as "You shall have no other gods before me". The problem as I see it is that Christians only see law as being the law of Moses. Christ was more than just the savior; he is also the lawgiver. But apparently many think that doesn't mean what it means.