What is the single theme of the book of Galatians?
The single theme of Galatians is that the believer is not under Law but under Grace. The entire six chapters of the book are devoted to that one theme alone. Paul constantly refers to Abraham, using Isaac and Ishmael as pictures of Law and Grace, appealing to Jews to leave legalism and enter God's Grace.
Les teaches that the whole six chapters of Galatians are on that one theme alone: the believer is not under Law but under Grace. When teaching Galatians, he points out that Paul constantly referred to Abraham and used the allegory of Isaac and Ishmael as pictures of Law and Grace. Paul kept flipping back into the Old Testament, using the Jew as examples and appealing to them to come out of their blindness and legalism and step into the Light of God's Grace. This covered the period while Paul was roaming the Roman Empire establishing churches, until the interruption at Acts 28, when he was arrested and taken to prison in Rome.