Not by works of righteousness which we have done, but according to his mercy he saved us, by the washing of regeneration, and renewing of the Holy Ghost.
You have here a commendation of Baptism such as I can hardly find anywhere else in the New Testament. The enemies of the grace of God, under the pretext of love, have preceded us and distorted all those other passages. Therefore this passage summarized those. By mercy, he says, we are saved. But by what road does mercy come to us? By washing. They say: "Washing can refer to the Word, the Gospel, the Holy Sprit, namely, that we are baptized in the Spirit. If He is conferred, then Baptism is a washing of regeneration, that is, it is a sign of those who are regenerated. In other words, the washing of regeneration is bestowed on those who have already been regenerated through the Holy Spirit." If we say: "By what authority do you establish this as the meaning?" there is no one at home. Therefore they say that no outward thing justifies or profits a person. But Baptism with water is such a thing; and therefore where ever it is said of Baptism that it justifies, they add a gloss, as, for example, in the passage from Peter (1 Peter 3:21), which they take to mean: "You have had a seal impressed upon you by which it is declared that you have been baptized through the Holy Spirit." I can practice this art too, and better than they, but I ask them to prove it. Therefore I could say: "The blood of Christ does not profit us, because it is an outward thing. Christ was conceived [by the Holy Spirit], as we pray; therefore He does not profit us." This is their foolishness. We, too, say that an outward thing is nothing, if it is by itself; then it is utterly [without profit]. But if it is joined to the very will of God, then it does profit because of the will that has been attached to it. One cannot convince the sectarians of this, and to this argument they do not answer a word except to stick to their refrain about "an outward thing." Why do they teach this? We know. But if God binds His Word to a tree, it now becomes not only an outward thing, but through the Word there is the presence, will, and mercy of God. Thus in Baptism there is not only mere water, because there is present here the name, or all the divine power joined through the Word in Baptism, and God Himself is the One who baptizes. Take note of this. But they do not listen, but stubbornly harp on the words: "An outward thing does not [do it]." Beware of their madness, because when an outward thing is grasped through the Word of God, it is a saving thing. If the humanity of Christ were without the Word, it would be a vain thing. But now we are saved through His blood and His body, because the Word is joined to it. Thus Baptism bears the Word of God by which the water is sanctified, and we are sanctified in the water." Martin Luther, Commentary on Titus.