What was the whole purpose of Paul's letter to the Galatians?
The whole purpose was to prove to Gentile believers in Galatia that they were not under the Mosaic Law but under grace. It addressed their desire to return to the weak and beggarly elements of the Law, showing why a believer who tasted grace should not go back into bondage.
Les explains that the whole thrust of the little book of Galatians was to prove to the Gentile believers up in Galatia that they were not under the Mosaic Law but under grace. He points out Paul was dealing with their desire to turn again to the weak and beggarly elements and be in bondage, and Paul strongly opposed it, even saying he could raise his voice against them. Les asks why a believer who has tasted of grace would want to go back under the Law, emphasizing the difference between Law and grace.
Howbeit then, when ye knew not God, ye did service unto them which by nature are no gods.