We, therefore, profess that it is necessary that the Law be begun in us, and that it be observed continually more and more. And at the same time we comprehend both spiritual movements and external good works [the good heart within and works without]. Therefore the adversaries falsely charge against us that our theologians do not teach good works while they not only require these, but also show how they can be done [that the heart must enter into these works, lest they be mere, lifeless, cold works of hypocrites]. The result convicts hypocrites, who by their own powers endeavor to fulfil the Law, that they cannot accomplish what they attempt. [For are they free from hatred, envy, strife, anger, wrath, avarice, adultery, etc.? Why, these vices were nowhere greater than in the cloisters and sacred institutes.] For human nature is far too weak to be able by its own powers to resist the devil, who holds as captives all who have not been freed through faith. There is need of the power of Christ against the devil, namely, that, inasmuch as we know that for Christ’s sake we are heard, and have the promise, we may pray for the governance and defense of the Holy Ghost, that we may neither be deceived and err, nor be impelled to undertake anything contrary to God’s will. [Otherwise we should, every hour, fall into error and abominable vices.] Just as Ps. 68:18 teaches: Thou hast led captivity captive; Thou hast received gifts for man. For Christ has overcome the devil, and has given to us the promise and the Holy Ghost, in order that, by divine aid, we ourselves also may overcome. And 1 John 3:8: For this purpose the Son of God was manifested, that He might destroy the works of the devil. Again, we teach not only how the Law can be observed, but also how God is pleased if anything be done, namely, not because we render satisfaction to the Law, but because we are in Christ, as we shall say after a little. It is, therefore, manifest that we require good works. Yea, we add also this, that it is impossible for love to God, even though it be small, to be sundered from faith, because through Christ we come to the Father, and the remission of sins having been received, we now are truly certain that we have a God, i.e., that God cares for us; we call upon Him, we give Him thanks, we fear Him, we love Him as 1 John 4:19 teaches: We love Him, because He first loved us, namely, because He gave His Son for us, and forgave us our sins. Thus he indicates that faith precedes and love follows. Likewise the faith of which we speak exists in repentance, i.e., it is conceived in the terrors of conscience, which feels the wrath of God against our sins, and seeks the remission of sins, and to be freed from sin. And in such terrors and other afflictions this faith ought to grow and be strengthened. Wherefore it cannot exist in those who live according to the flesh who are delighted by their own lusts and obey them. Accordingly, Paul says, Rom. 8:1: There is, therefore, now no condemnation to them that are in Christ Jesus, who walk not after the flesh, but after the Spirit. So, too, Rom 8:12-13: We are debtors, not to the flesh, to live after the flesh. For if ye live after the flesh, ye shall die; but if ye, through the Spirit, do mortify the deeds of the body, ye shall live. Wherefore, the faith which receives remission of sins in a heart terrified and fleeing from sin does not remain in those who obey their desires, neither does it coexist with mortal sin.
Apology (Defense) of the Augsburg Confession, Article V, 15-23.