The Christian belief that baptism is necessary for salvation is so unshakable that even the Protestant Martin Luther affirmed the necessity of baptism. He wrote: "Baptism is no human plaything but is instituted by God himself. Moreover, it is solemnly and strictly commanded that we must be baptized or we shall not be saved. We are not to regard it as an indifferent matter, then, like putting on a new red coat. It is of the greatest importance that we regard baptism as excellent, glorious, and exalted" (Large Catechism 4:6).

Yet Christians have also always realized that the necessity of water baptism is a normative rather than an absolute necessity. There are exceptions to water baptism: It is possible to be saved through "baptism of blood," martyrdom for Christ, or through "baptism of desire", that is, a conscious or even unconscious desire for baptism.

Thus the Catechism of the Catholic Church states: "Those who die for the faith, those who are catechumens, and all those who, without knowing of the Church but acting under the inspiration of grace, seek God sincerely and strive to fulfill his will, are saved even if they have not been baptized" (CCC 1281; the salvation of unbaptized infants is also possible under this system; cf. CCC 1260–1, 1283).