What is the main theme of the book of Galatians?

Les explains that he likes to review and remind his audience why this little letter was written. The whole theme of the letter to the Galatian church is that we are not under law but under grace. That statement came straight from the lips of the Apostle Paul, first and foremost; until then it was an unknown tenet. Les notes that even Peter, for the most part, had no comprehension of this great move of God to come away from Israel and the covenant promises and go out to the whole world—black and white, rich and poor, east and west, Jew or Gentile—with the tremendous gospel of the grace of God. He adds that this is hard for many people to swallow. Some claim there is no difference between Peter's message and Paul's, but Les says the difference is daylight and dark. Later, Peter himself wrote in his second epistle that the things written by Paul are hard to be understood.