In Baptism there is the promise of salvation (Mark 16:16): “He who believes, etc.” If anyone denies here, as the fanatical spirits do today, that righteousness and salvation are granted to an infant as soon as he is baptized; if anyone evades this promise in this way by saying that it becomes valid when a man reaches the use of reason and is able to do good works and to obtain what is set forth in the promise by doing good works; if anyone says that Baptism is not a sign of the will of God toward us but only a mark that distinguishes believers from unbelievers – such a person utterly deprives Baptism of salvation and attributes salvation to works.
Martin Luther, Luther’s Works 26, 241-242