1 - Paul is concerned the Galatians are turning from the Gospel. False teachers be damned!
1-2 - Paul isn't pleasing men. He gives his biography to show he isn't under the other apostles. They added nothing to his ministry, but confirmed it. He even had to rebuke Peter once.
2 - We are justified and live by faith in Christ, not by trying to keep the law
3 - Abraham believed God's promise. We live the same way as Abraham's children. The law convicts us of sin, and Jesus redeems us from its curse. The law cannot give or make us righteous.
4 - You are a son and heir of God because Christ took the curse of the law for us. Why go back to being a slave? You latched on to me and my gospel at first but now you spurn me. We are children of the free grace covenant mother Sarah, not the law-bondage covenant mother Hagar.
5 - if you trust circumcision, you don't need the cross. Don't use your freedom to hurt, but to heal each other. Spirit and flesh fight each other. Be led by Spirit, not flesh.
6 - circumcision zealots are in it for the PR. Don't give in. Boast only in the cross.