12 L. We pardon a layman because, when he was baptized, he had a sincere impression that he was joining the Church. He believed and was baptized in accordance with his faith.
O. That is something new for a man to be made a Christian by one who is not a Christian. When he joined the Arians into what faith was he baptized? Of course into that which the Arians held. If on the other hand we are to suppose that his own faith was correct, but that he was knowingly baptized by heretics, he does not deserve the indulgence we grant to the erring. But it is quite absurd to imagine that, going as a pupil to the master, he understands his art before he has been taught. Can you suppose that a man who has just turned from worshipping idols knows Christ better than his teacher does? If you say, he sincerely believed in the Father, and the Son, and the Holy Ghost, and therefore obtained baptism, what, let me ask, is the meaning of being sincerely ignorant of what one believes? He sincerely believed. What did he believe? Surely when he heard the three names, he believed in three Gods, and was an idolater; or by the three titles he was led to believe in a God with three names, and so fell into the Sabellian heresy. Or he was perhaps trained by the Arians to believe that there is one true God, the Father, but that the Son and the Holy Spirit are creatures. What else he may have believed, I know not: for we can hardly think that a man brought up in the Capitol would have learned the doctrine of the co-essential Trinity. He would have known in that case that the Father, Son, and Holy Spirit are not divided in nature, but in person. He would have known also that the name of Son was implied in that of Father and the name of Father in that of Son. It is ridiculous to assert that any one can dispute concerning the faith before he believes it; that he understands a mystery before he has been initiated; that the baptizer and the baptized hold different views respecting God. Besides, it is the custom at baptism to ask, after the confession of faith in the Trinity, do you believe in Holy Church? Do you believe in the remission of sins? What Church do you say he believed in? The Church of the Arians? But they have no Church. In ours? But the man was not baptized into it: he could not believe in that whereof he was ignorant.
L. I see that you can prattle cleverly about each point that I raise; and when we let fly a dart you elude it by a harangue which serves you for a shield; I will therefore hurl a single spear which will be strong enough to pierce your defences and the hail-storm of your words. I won't allow strength any longer to be overcome by artifice. Even a layman baptized without the Church, if he be baptized according to the faith, is received only as a penitent: but a bishop either does no penance and remains a bishop, or, if he does penance he ceases to be a bishop. Wherefore we do right both in welcoming the penitent layman, and in rejecting the bishop, if he wishes to continue in his office.
O. An arrow which is discharged from the tight-drawn bow is not easy to avoid, for it reaches him at whom it was aimed before the shield can be raised to stop it. On the other hand your propositions are pointless and therefore cannot pierce an opponent. The spear then which you have hurled with all your might and about which you speak such threatening words, I turn aside, as the saying is, with my little finger. The point in dispute is not merely whether a bishop is incapable of penitence and a layman capable, but whether a heretic has received valid baptism. If he has not (and this follows from your position), how can he be a penitent, before he is a Christian? Show me that a layman coming from the Arians has valid baptism, and then I will not deny him penitence. But if he is not a Christian, if he had no priest to make him a Christian, how can he do penance when he is not yet a believer?
Source: The Dialogue Against the Luciferians (New Advent)