What is the theme in Paul's letter to the Thessalonians?

The theme of Galatians is that the Law is no longer in effect. We are in the age of grace and salvation is by faith in Jesus Christ, not in keeping the law. Christ fulfilled the law and now we don't need this to reveal to us our sins, We as Christians have the Holy Spriit dwelling within us to convict us and teach us how we should live. Ch5:1 tells us we have liberty in Christ. Not to sin, but to be free to live for Christ. Santification is through the Spirit not the law. I hope this might help someone