What is Baptism according to the witness of the New Testament? What does it give or what is the good of it? How is Baptism related to the faith of the one to be baptized? Is it necessary for salvation or not? What may we answer first of all is that according to the clear teaching of the New Testament Baptism is the “washing of regeneration.” The early church, which always simply identified Baptism with regeneration, and the church of all times, with the exception of the Reformed communities, have understood Titus 3: 5 in this way— and rightly so. There Baptism is “the washing of regeneration and renewal in the Holy Spirit.” In Baptism the Holy Spirit is bestowed; we are “baptized into one body” (1   Cor. 12: 13). According to Rom. 6: 3, the baptized are baptized into Christ’s death. Those are all realities that happen not alongside of Baptism but in it. Water Baptism in the New Testament, as long as it is Baptism into Christ, in the name of Christ, is Spirit Baptism; it is being born anew and at the same time from above “of water and the Spirit” (John 3: 5). The New Testament knows nothing of a being born again without Baptism or apart from Baptism. Baptism is therefore not a sign but a means of regeneration. To regard it only as a sign of a regeneration that also may take place without it or apart from it is unbiblical.

What is it that prompts the Reformed doctrine? We may observe something similar in the doctrine of the Lord’s Supper. On the one hand the pure symbolism of Zwingli is rejected. He saw Baptism as merely a sign professing that one is a Christian, just as the white cross worn on the garment of a Swiss Confederate made him recognizable as a Swiss Confederate [LCC 24: 131]. On the other hand, along with the Roman sacramental doctrine of an opus operatum, the Lutheran— and New Testament— identification of sign and action is also rejected. At the bottom of all this lies the antipathy of Calvin and his predecessors in medieval theology against the idea that an external, physical action can produce spiritual effects, such as the forgiveness of sins. This is first of all a secular, philosophical presupposition, and second, it misunderstands the significance of the Word of God in Baptism. “For without the Word of God the water is simple water and no Baptism. But with the Word of God it is Baptism, that is, a gracious water of life and a washing of regeneration” (SC IV).

Also in Catholic doctrine the Word as the forma is inseparably tied up with the sacrament; indeed, it is what makes the sacrament a sacrament. This is in harmony with the words of Augustine, which time and again are quoted by all churches in the West: “The word comes to the element and makes the sacrament.” Where Luther differs from the Catholic doctrine of Baptism he says himself in the Smalcald Articles, distinguishing himself from both the Thomists and the Scotists: We do not agree with Thomas and the Dominicans who forget the Word [God’s institution] and say that God has joined to the water a spiritual power which, through the water, washes away sin. Nor do we agree with Scotus and the Franciscans who teach that Baptism washes sin away through the assistance of the divine will, as if the washing takes place only through God’s will and not at all through the Word and water. (SA III V 2– 3).

With Luther everything depends on the intimate connection of Word and water: “God is surely a God of life. Because He is there in this water, it cannot but be the very water of life, which puts death and hell to flight and makes alive with the life that has no end” (WA 52: 102.29). Luther has no need to demonstrate first that this presence of God or Christ can be no other presence than that which happens in His Word. All effects of Baptism are effects of the Word combined with the water for Luther and the Lutheran Church. The Reformed opposition to this Lutheran understanding of Baptism is therefore nothing else than opposition to the Lutheran doctrine of the means of grace as a whole. They are opposing the fact that God does not give His Spirit, and therewith forgiveness of sins, life and salvation, to anyone apart from the external means of His grace, apart from the external Word, apart from Baptism, or apart from the Lord’s Supper. “The power of Jesus Christ, which is the only power of Baptism, is not bound to the administration of Baptism” (Barth, 14f.). … As was often the case, Luther’s way was the lonely way between Rome and the Enthusiasts. Over against the Enthusiasts, among whom he lumped Zwingli and his followers, as he would also have done with the Calvinists had they been part of his experience, he firmly held to the Sacrament of Baptism and everything that belongs with it: infant Baptism, necessity for salvation, and regeneration. Over against Rome he firmly held to the sola fide: Forgiveness of sins, life, and salvation are given only to faith. Just as in the Sacrament of the Altar only he receives forgiveness of sins and so also life and salvation who has faith in “these words,” that is, in the promise: “Given and shed for the forgiveness of sins,” so it is true of Baptism: “It works forgiveness of sins, delivers from death and the devil and gives eternal salvation to all who believe this, as the words and promises of God declare.” And this is not talking about some future faith that is then confessed at confirmation, so that this would be a necessary completion of Baptism. … Luther goes his lonely way between the hierarchical safeguards of Rome and the psychological safeguards of the Enthusiasts. It is the lonely way of the reformer, who heeds only the Word and God and counts on this Word for everything, even for what is humanly impossible. Only in this way can he and the Lutheran Church hold together the objectivity of the sacrament and the sola fide, whereby we do not forget that justifying faith

— Herman Sasse. Letters to Lutheran Pastors-Volume 1: Letter 4: Holy Baptism. Concordia Publishing House. Kindle Edition. 2013.