That is what I love about Luther's commentary. Luther was learning this stuff and loving it as he was teaching it. He was not a theologian who had the benefit of walking in the steps of bible-loving, grace-espousing mentors. He was pierced by the word and the Spirit changed his heart by it. This is what you see in Galatians. During my study I read many great commentaries, but my favorite was Luthers. Luther acts in this commentary as both an exegete and a pastor. This is a commentary that you may just want to curl up with on the couch after you finish studying a section and read and read again. His passion is contagious.
(By the way, my other favorite Galatians commentaries were MacArthur's and Hendriksen's. Calvin's and Stott's came in a close #4 and #5). I hope this helps.
Luther's Commentary on Galatians in the history of the Christian Church is very remarkable. It presents like no other of the central thought of Christianity: the justification of the sinner for the sake of Christ's merits alone. Luther also delineates the difference between Law (what God demands from us) and Gospel (what God has done and does for us); in this text, we understand his "simul justus et peccator," that is, a Christian is simultaneously 100 % saint and 100 % sinner.
To understand Christian theology and justification by faith, reading this commentary is proper, right, for our eternal good--for Luther explains the doctrines of the Scriptures in forthright boldness and clarity.