In the second place, since we know now what Baptism is, and how it is to be regarded, we must also learn why and for what purpose it is instituted; that is, what it profits, gives, and works. And this also we cannot discern better than from the words of Christ above quoted: He that believeth and is baptized shall be saved.
Therefore state it most simply thus, that the power, work, profit, fruit, and end of Baptism is this, namely, to save. For no one is baptized in order that he may become a prince, but, as the words declare, that he be saved.
But to be saved, we know, is nothing else than to be delivered from sin, death, and the devil, and to enter into the kingdom of Christ, and to live with Him forever.” Martin Luther in the “Large Catechism” in the “Book of Concord” – still used by the Lutheran Church.
John Calvin wrote “all who are clothed with the righteousness of Christ are at the same time regenerated by the Spirit, and that we have an earnest of this regeneration in baptism” (5.12.1. Institutes of the Christian Religion)