Exodus 4:10

[Moses] believes that by God's will he can suddenly become eloquent when he says, "or since the time you began to speak to your servant." He shows that it could happen that one who was not eloquent the day before, or the day before that, could suddenly become eloquent, from the time when the Lord began to speak to him.

And of old indeed Moses said: "but I am ἄλογος (without speech or reason)" — which, though the Latin has rendered it otherwise, can nevertheless be more properly translated: "without speech or reason" —, and after he said this, he received reason or speech, which he had confessed that he did not before possess. But the people of Israel in Egypt, before it received the law, was in a certain way "mute", without speech and reason; then it received speech, of which Moses was an image. This people, therefore, does not now confess what it then confessed in Moses, namely that it is "mute" and ἄλογος, but by nods and silence indicates that it does not have speech and does not have reason. Does it not seem to you to be a confession of foolishness, when none of them can render a reason for the legal precepts and the prophetic oracle?

But I will bring forward to you yet another thing, which you cannot contradict. In Exodus, where we in the books of the Church have it written that Moses answered the Lord and said: "Provide, Lord, another whom you may send. For I am of a thin voice and slow of tongue," you in the Hebrew copies have: "but I am uncircumcised in lips." Behold, you have circumcision of the lips according to your copies, which you say are truer. If, then, according to you Moses says he is still unworthy, because he is not circumcised in lips, it is certain that he thereby indicates this, that he is worthier and holier who is circumcised in lips. Apply, then, the sickle also to your lips and cut away the coverings of your mouth, since such an understanding in the divine letters pleases you. But if you recall the circumcision of the lips to allegory, and likewise call the circumcision of the ears allegorical and figurative, how do you not also seek an allegory in the circumcision of the foreskin?