John Murray: Why is justification by faith alone?

John Murray brilliantly summarizes why justification is by faith alone:

There are apparent reasons why justification is by faith and by faith alone. First, it is altogether consonant with the fact that it is by grace. “Therefore it is of faith, in order that it might be according to grace” (Rom. 4:16). Faith and grace are wholly complementary. Second, faith is entirely congruous with the fact that the ground of justification is the righteousness of Christ. The specific quality of faith is that it receives and rests upon another, in this case Christ and his righteousness. No other grace, however important it may be in connection with salvation as a whole, has this as its specific and distinguishing quality. We are justified therefore by faith. Third, justification by faith and faith alone exemplifies the freeness and richness of the gospel of grace. If we were to be justified by works, in any degree or to any extent, then there would be no gospel at all. For what works of righteousness can a condemned, guilty and depraved sinner offer to God? That we are justified by faith advertises the grand article of the gospel of grace that we are not justified by works of law. Faith stands in antithesis to works; there can be no amalgam of these two (cf. Gal. 5:4). That we are justified by faith is what engenders hope in a convicted sinner’s heart. He knows he has nothing to offer. And this truth assures him that he needs nothing to offer, yea, it assures him that it is an abomination to God to presume to offer. We are justified by faith and therefore simply by entrustment of ourselves, in all our dismal hopelessness, to the Saviour whose righteousness is undefiled and undefilable. Justification by faith alone lies at the heart of the gospel and it is the article that makes the lame man leap as an hart and the tongue of the dumb sing. Justification is that by which grace reigns through righteousness unto eternal life; it is for the believer alone and it is for the believer by faith alone. It is the righteousness of God from faith to faith (Rom. 1:17; cf. 3:22). (John Murray, Redemption Accomplished and Applied (Grand Rapids: Eerdmans, 1955), 130-131; quoted by Brian Schwertley in his refutation of the Auburn Avenue theology)