Paul starts how the Gospel is a revelation of Jesus Christ, not something he made up or received from man, but rather was taught by God. (Galatians 1:1, 11-12)
Paul says if anyone preaches a “gospel” contrary to the one and only true Gospel that Jesus revealed, that person is to be eternally accursed. It doesn’t matter who you are, apostle, or angel, if you preach a different “gospel” you are accursed. (Galatians 1:6-9)
We find out we are not justified, or legally declared righteous by God, by our works, or even keeping God’s law. But rather Jesus Christ, and faith alone in him, that is what justifies us. If we think it is by the law, than Christ died in vain. (Galatians 2:16-21)
Paul argues that Abraham was blessed by faith in God, and so will we. (Galatians 3:7-9)
If we try to keep the whole law for justification, then we are cursed, because no one can ever keep the law. However Christ, became a curse for us to redeem us from the law. The Old Testament says that if anyone hangs on a cross/tree that person is accursed according to the law. (Galatians 3:10-13)
Paul shows how Abraham received the promise over 400 years before the law. And he shows the law was given not to justify us, but to expose our sin and point us to Jesus. (Galatians 3:15-22)
