25 Now a discussion arose between John’s disciples and the Jews over purifying.
The Holy Bible: English Standard Version. (2016). (John 3:25). Wheaton, IL: Crossway Bibles.
Since the beginning of the world the question has been raised and hotly debated whether salvation is attained by God’s grace or by works. The chief purification must precede, for “grace and truth come through Jesus Christ” (John 1:17). Furthermore, “from His fullness have we all received, grace upon grace” (John 1:16). After that we do not forbid good works. However, we do preach that good works can neither constitute nor bring about this purification. But Christ must purify us with His blood; then the other purification will follow from grace, Thus we come away from the Jordan and the Dead Sea.
Now John introduces a new mode of purification, one hitherto unknown to the Jews. In addition, he proclaimed the message that the people must desist from their evil deeds and life and await the coming Messiah. Such testimony implied that he himself was not the one who could purify them, and that his Baptism was not the purification. He says: “I purify with water. I do not claim that you are cleansed thereby. No, you are cleansed by Him who comes after me, who will purify you with the Holy Spirit.” At the same time those who had died before this were saved by accepting John’s Baptism and being purified through their faith in the advent of Christ, to whom John pointed as the true Purifier. In this way all the patriarchs and prophets were purified. Circumcision and all purification were associated with, and related to, the coming Messiah. Circumcision helped them inasmuch as it was linked to the coming Messiah; they were circumcised on their faith in Him, and thus they were saved. Otherwise they would not have been saved. And Cain, who presumed to be everything, is nothing; for his faith does not rely on the future Seed of the woman. It is Abel who is purified, not Cain.
About this a horrible quarrel ensued, so that in the end he who wanted to be everything slew Abel. This has always been the course of history. Just read the records, and see how all the patriarchs and fathers sacrificed and how the fire consumed their offerings. Then the ungodly Jews remarked: “God regards the gift and the sacrifice!” Now Cain had offered nothing but chaff. However, God is not interested in oxen, sheep, and sacrifices; as is evident from Ps. 50:8–9 and from Is. 1:11. God says: “Who commanded you to sacrifice?”
The trouble is, as we see from the books of all the prophets, that the ungodly assume they are purified because of their generous sacrifices; but God is of a different mind. Because of the assumption of the ungodly all the prophets were tortured and slain, and all the great kings dethroned. But whoever bore in mind during his sacrifice that the true Lamb, Christ, was to be slaughtered for the sins of the world, was saved by and in that faith in the advent of Christ. And whoever failed to do so was not saved. Even if such a person were willing to sacrifice a thousand oxen, it would be regarded by God as little as a fly. In the case of the godly, however, what availed was their reliance on the future Seed for their salvation. Thus from Adam and Abel down to our day there is but one way to salvation, for the promise of Christ and the Christian faith began with the promise that the woman’s Seed should crush the serpent’s head. This promise endured until He Himself appeared. And now faith no longer applies to the future Christ but to the present Christ, the Christ who has come. And what was formerly observed in the Law has validity no longer, whether it be Law or circumcision. Christ Himself is present now, and everything pointed to Him.
Luther, M. (1999). Luther’s works, vol. 22: Sermons on the Gospel of St. John: Chapters 1-4. (J. J. Pelikan, H. C. Oswald, & H. T. Lehmann, Eds.) (Vol. 22, pp. 426–428). Saint Louis: Concordia Publishing House.