8 But now observe how more tolerable in comparison with us is the lying of the Priscillianists, when they know that they speak deceitfully: whom by our own lying we think right to deliver from those false things in which they by erring are decayed. A Priscillianist says, that the soul is a part of God, and of the same nature and substance with Him. This is a great and detestable blasphemy. For it follows that the nature of God may be taken captive, deceived, cheated, disturbed, and defiled, condemned and tortured.
But if that man also says this, who from so great an evil desires to deliver a man by a lie, let us see what is the difference between the one blasphemer and the other. “Very much,” do you say: “for this the Priscillianist says, also believing it so: but the catholic not so believing, though so speaking.” The one, then, blasphemes without knowing, the other with knowledge: the one against science, the other against conscience; the one has the blindness of thinking false things, but in them has at least the will of saying true things; the other in secret sees truth, and willingly speaks false.
“But the one;” you will say, “teaches this, that he may make men partakers of his error and madness: the latter says it that from that error and madness he may deliver men.” Now I have already shown above how hurtful is this very thing which people believe will do good: but meanwhile if we weigh in these two the present evils, (for the future good which a catholic seeks from correcting a heretic is uncertain,) who sins worse? Who deceives a man without knowing it, or he who blasphemes God, knowing it?
Assuredly which is the worse, that man understands, who with solicitous piety preferrs God to man. Add to this, that, if God may be blasphemed in order that we may bring men to praise Him, without doubt we do by our example and doctrine invite men not only to praise, but also to blaspheme God: because they whom through blasphemies against God we plot to bring to the praises of God, verily, if we do bring them, will learn not only to praise, but also to blaspheme. These be the benefits we confer on them whom, by blaspheming not ignorantly but with knowledge, we deliver from heretics!
And whereas the Apostle delivered men to Satan himself that they might learn not to blaspheme, we endeavor to rescue men from Satan, that they may learn to blaspheme not with ignorance, but with knowledge. And upon ourselves, their masters, we bring this so great bane, that, for the sake of catching heretics, we first become, which is certain, blasphemers of God, in order that we may for the sake of delivering them, which is uncertain, be able to be teachers of His truth.
Source: To Consentius: Against Lying (New Advent)