J. Gresham Machen, 1925:
I am not at all ashamed to speak, even in this day and generation, of 'the doctrine of justification by faith.' It should not be supposed, however, that that doctrine is an abstruse or intricate thing. On the contrary it is a very simple thing, and it is instinct with life.
It is an answer to the greatest personal question ever asked by a human soul--the question: 'How shall I be right with God; how do I stand in God's sight; what what favour does he look upon me?' There are those, it must be admitted, who never raise that question; there are those who are concerned with the question of their standing before men, but never with the question of their standing before God; there are those who are interested in what 'people say,' but not in the question what God says. Such men, however, are not those who move the world; they are apt to go with the current; they are apt to do as others do; they are not the heroes who change the destinies of the race. The beginning of true nobility comes when a man ceases to be interested in the judgment of men, and becomes interested in the judgment of God. (What Is Faith? p. 163)
This is wonderfully helpful. Machen is connecting the dots for us between justification by faith and one of the greatest struggles in this life, the temptation to seek the approval of people, something I'm thoroughly acquainted with myself. Justification by faith is not the idea that as long as we maintain the minimum intensity of faith, we'll be justified. 'Just have enough faith!' That is to turn justification by faith into its opposite. It is to make this doctrine self-dependent, the very thing the doctrine is turning upside down. Justification by faith is 'justification by God' and justification by works is 'justification by self.' Faith says: I will find my okay-ness in God's solid and sure gift of Christ rather than the wavering and fickle but alluring promises of idolatry, such as man-approval. Justification by faith gives us the resources now, emotionally and psychologically, to relinquish the need for human approval. Machen saw that.
Maybe Machen's insight helps us see why Paul begins Galatians, his charter on Christian liberty, his clearest statement of justification by faith, by declaring that he is not now trying to win the approval of men (1:10).