Gal 1:
The grace of Christ was the true gospel.
In Matthew 4:15-23, Jesus began his ministry with the Gospel message to repent for the Kingdom of God is at hand, which was a light to the Gentiles, and the Torah was how his audience knew what sin is (Romans 3:20), so repenting from our disobedience to it is a central part of the Gospel of the Kingdom/Grace, which Paul also taught based on the Torah:
Acts 14:21-22 When they had preached the gospel to that city and had made many disciples, they returned to Lystra and to Iconium and to Antioch, 22 strengthening the souls of the disciples, encouraging them to continue in the faith, and saying that through many tribulations we must enter the kingdom of God.
Acts 21:24-25 4 But I do not account my life of any value nor as precious to myself, if only I may finish my course and the ministry that I received from the Lord Jesus, to testify to the gospel of the grace of God. 25 And now, behold, I know that none of you among whom I have gone about proclaiming the kingdom will see my face again.
Acts 28:23 When they had appointed a day for him, they came to him at his lodging in greater numbers. From morning till evening he expounded to them, testifying to the kingdom of God and trying to convince them about Jesus both from the Law of Moses and from the Prophets.
Romans 15:4 For whatever was written in former days was written for our instruction, that through endurance and through the encouragement of the Scriptures we might have hope.
Romans 15:18-19 For I will not venture to speak of anything except what Christ has accomplished through me to bring the Gentiles to obedience—by word and deed, 19 by the power of signs and wonders, by the power of the Spirit of God—so that from Jerusalem and all the way around to Illyricum I have fulfilled the ministry of the gospel of Christ;
Paul stated in the next chapter 2:
In Romans 3:28-31, Paul contrasted a law of works with a law of faith, so works of the law are of works while he said that our faith upholds the Law of God, so it is of faith, which again is in contrast with work of the law that are not of faith (Galatians 3:10-12).
According to Deuteronomy 27-28, relying on the Torah is the way to be blessed while not relying on it is the way to be cursed, so Galatians 3:10 should not be interpreted as Paul quoting from Deuteronomy 27-28 to support a point that is arguing against it by saying that relying on it is the way to be cursed and not relying on it is the way to be blessed. Rather, not relying on the Torah is the way to be cursed, which is why all who rely on works of the law instead come under a curse.
He contrasted works of the law and faith in Christ.
It is contradictory to contrast having faith in God's word with having faith in God's word made flesh. In Deuteronomy 27-28, it lists the blessing of being a doer of the Torah and the curse of not being a doer of it, so being set free from the curse of the Torah is being set free from not being a doer of it so that we can be free to enjoy the blessing of being a doer of it through faith in Christ.
If God freed the Israelites from slavery in Egypt in order to put them under slavery to the Torah, then it would be for slavery that God sets us free, however, Galatians 5:1 says that it is for freedom that God's set us free and Psalms 119:45 says that the Torah is of freedom. In Psalms 119:142, the Torah is truth, and in John 8:31-36, it is the transgression of the Torah that puts us into slavery while the truth sets us free.
Do not be burdened by the old law but be free in Christ.
What gospel did Paul preach to the Galatians?
Believers are no longer bound by Moses' law; we are justified or saved by faith in Christ.
See also
JUSTIFICATION by works, grace, or faith?
In Titus 2:14, it does not say that Jesus gave himself to free us from the Torah, but in order to free us from all lawlessness and to purify for himself a people of his own possession who are zealous for doing good works, so becoming zealous for doing good works in obedience to the Torah is the way to believe in the Gospel that Jesus and Paul taught and in what Jesus accomplished through the cross while refusing to obey the Torah is the way to reject everything that Jesus accomplished. 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 Torah, 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. Again the Torah is how we have knowledge of what sin is (Romans 3:20), so the position that we are not required to obey the Torah is the position that we do not need salvation from sin, that we do not need the Gospel that Jesus and Paul taught, and that we do not need Jesus to have given himself to redeem us from all lawlessness.
