This one comes from Melanchthon’s Apology of the Augsburg Confession, Article IV, 164A, 172B, ht SMZ:

Philipp_Melanchthon_monument“[I]f we had to believe that after our renewal we must become acceptable not by faith on account of Christ but on account of our keeping of the law, our conscience would never find rest. Instead, it would be driven to despair. For the law always accuses since we never satisfy the law… For who loves or fears God enough? Who endures patiently the afflictions imposed by God? Who does not often doubt whether human affairs are ruled by the counsel of God? Who does not often doubt whether one is heard by God? Who is not often angry that the wicked enjoy a better lot than the pious and that the godly are oppressed by the wicked? Who is not often enraged by the judgment of God when he seems to abandon us? How many live up to their calling? How many love their neighbor as themselves? Who is not incited by concupiscence? About these sins the psalms says [Ps. 32:6], ‘Therefore let all who are the saints offer prayer to you.’ Here he says that the saints pray for the forgiveness of sins.’ … Only faith brings [peace to consciences] – faith which is confident that on account of Christ the high priest we have a gracious God… Faith justifies in this way: that it simultaneously makes alive, that is, it cheers and consoles consciences and produces eternal life and joy in the heart.”