What was St. Paul angry about in the letter to the Galatians?

In my opinion, he was writing in an attempt to correct inappropriate doctrine and practice among the Galatians. They were being Judaized - being sold the notion of relying on keeping the Jewish law instead of receiving salvation by faith in Jesus.

Galatians 1:6,7

6I marvel that ye are so soon removed from him that called you into the grace of Christ unto another gospel:

7Which is not another; but there be some that trouble you, and would pervert the gospel of Christ.

Galatians 3:2,3

2This only would I learn of you, Received ye the Spirit by the works of the law, or by the hearing of faith?

3Are ye so foolish? having begun in the Spirit, are ye now made perfect by the flesh?