There are few books that have profited me more – especially in moments of existential crises of faith – than Martin Luther’s Commentary on Galatians. It can be downloaded for free here if you have a Kindle or the app or the like.
To whet your appetite:
The world bears the Gospel a grudge because the Gospel condemns the religious wisdom of the world. Jealous for its own religious views, the world in turn charges the Gospel with being a subversive and licentious doctrine, offensive to God and man, a doctrine to be persecuted as the worst plague on earth. As a result we have this paradoxical situation: The Gospel supplies the world with the salvation of Jesus Christ, peace of conscience, and every blessing. Just for that the world abhors the Gospel. (Luther, Martin (2011-03-24). Commentary on the Epistle to the Galatians (Kindle Locations 43-47). . Kindle Edition.)
By His resurrection Christ won the victory over law, sin, flesh, world, devil, death, hell, and every evil. And this His victory He donated unto us. These many tyrants and enemies of ours may accuse and frighten us, but they dare not condemn us, for Christ, whom God the Father has raised from the dead is our righteousness and our victory. (Luther, Martin (2011-03-24). Commentary on the Epistle to the Galatians (Kindle Locations 91-93). . Kindle Edition.)
The article of justification must be sounded in our ears incessantly because the frailty of our flesh will not permit us to take hold of it perfectly and to believe it with all our heart… Grace remits sin, and peace quiets the conscience. Sin and conscience torment us, but Christ has overcome these fiends now and forever. (Luther, Martin (2011-03-24). Commentary on the Epistle to the Galatians (Kindle Locations 116-119). . Kindle Edition.)