Galatians 3: Who are the people of the Lord? trust vs ceremonial law

The Galatians believed in Jesus. There were signs that the Spirit was with them; however, they received Christian-Jews who told them that the ceremonial law, the circumcision, was necessary to be seen as the people of Lord. Why did they listen to these Christian-Jews? Because they were descendants of Abraham, because they were the people that received Moses and the prophets. Paul uses the Old Testament to argument that the Galatians are in fact the people of the Lord not by the law but by trusting in Jesus because:
Genesis 15:6 - Abraham was saved (seen as just by the Lord) by faith before the Law.
Genesis 12:3 - The promise to Abraham included all nations.
Deuteronomy 27:26 - The Law demands perfection (and we fail).
Habakkuk 2:4 - The righteous live by trusting God.

Therefore, the Galatians don't need to be circumcised to be accepted by the Lord. In fact, they were already accepted by the Lord when they trusted in Jesus, and it was notorious that the Spirit was with them.

5-6 Answer this question: Does the God who lavishly provides you with his own presence, his Holy Spirit, working things in your lives you could never do for yourselves, does he do these things because of your strenuous moral striving or because you trust him to do them in you? Don’t these things happen among you just as they happened with Abraham? He believed God, and that act of belief was turned into a life that was right with God.