These two sacraments may be received also by an unbeliever. Thus the devil would secretly teach us to build upon our works, and in order to accomplish this more easily he makes a sham of faith and says: If you do not believe then you are not baptized. But it simply does not follow that, if I do not obey my parents, therefore I have no parents; if I do not obey the government, therefore, the government is nothing. So it does not follow here: that person has not received baptism in faith, therefore, the baptism is nothing or is not genuine. Indeed, the baptism was genuine precisely because you did not rightly receive it. The abuse confirms the baptism: it does not deny it. If all of you here were to be baptized today and there were hardly three among you who were holy, the baptism would still not be false, but rather the contrary; for our work and misuse neither make nor unmake God’s work. A prince remains a prince, whether you are obedient or not. This the fanatics do not know, for they are blinded; that’s why they look at the sacrament without the Word. There is rebellion concealed in this mind, because it always wants to separate God’s Word from the person. It wants to tear down the Word; therefore it is a rebel, secretly.
Martin Luther, “On Baptism” from Sermons on the Catechism (1528) in John W. Doberstein (ed./tr.), Luther’s Works, vol. 51, Philadelphia: Muhlenberg Press/Fortress Press, 1959, pp. 187-88.