Faith alone lays hold of the promise, believes God when He gives the promise, stretches out its hand when God offers something, and accepts what He offers. This is the characteristic function of faith alone. Love, hope, and patience are concerned with other matters; they have other bounds, and they stay within these bounds. For they do not lay hold of the promise; they carry out the commands. They hear God commanding and giving orders, but they do not hear God giving a promise; this is what faith does.
Faith is the mother, so to speak, from whom that crop of virtues springs. If faith is not there first, you would look in vain for those virtues. If faith has not embraced the promises concerning Christ, no love and no other virtues will be there, even if for a time hypocrites were to paint what seem to be likenesses of them.
~ Martin Luther, Luther’s Works: Lectures on Genesis, Vol. 3 (1961)