“To get at the nature of that faith, or some other virtuous disposition? Here’s the way J. Gresham Machen answers this question in his 1925 book What Is Faith? ‘The true reason why faith is given such an exclusive place by the New Testament, so far as the attainment of salvation is concerned, over against love and over against everything else in man is that faith means receiving something, not doing something or even being something. To say, therefore, that our faith saves us means that we do not save ourselves even in slightest measure, but that God saves us.’

In other words, we are justified by faith alone, and not by love, because God intends to make it crystal clear that he does the decisive saving outside of us, and that the person and work of Christ are the sole ground of our acceptance with God.”

–John Piper, Think! The Life of the Mind and the Love of God