Luther on the Inseparability of Faith and Good Works
Faith, however is a divine work in us that changes us and makes us to be born anew of God, [John 1:12-12]. It kills the old Adam and makes us altogether different men, in heart and spirit and mind and powers; it brings with it the Holy Spirit. O, it is a living, busy, active, mighty thing, this faith. It is impossible for it not to be doing good works incessantly. It does not ask whether good works are to be done, but before the question is asked, it has already done them, and is constantly doing them. Whoever does not do such works, however, is an unbeliever. He gropes and looks around for faith and good works, but knows neither what faith is nor what good works are. Yet he talks and talks, with many words, about faith and good works.
Faith is a living, daring confidence in God’s grace, so sure and certain that the believer would stake his life on it a thousand times. This knowledge of and confidence in God’s grace makes men glad and bold and happy in dealing with God and all creatures. And this is the work that the Holy Spirit performs in faith. Because of it, without compulsion, a person is ready and glad to do good to everyone, to serve everyone, to suffer everything, out of love and praise to God, who has show him this grace. Thus it is impossible to separate works from faith, quite as impossible as to separate heat and light from fire.
–Martin Luther, from his Preface to St. Paul’s Epistle to the Romans, cited in the Solid Declaration of the Formula of Concord, IV. 10-12