1 Corinthians 14:11

"There are, it may be, so many kinds of voices in the world, and no kind is without signification:" i. e., so many tongues, so many voices of Scythians, Thracians, Romans, Persians, Moors, Indians, Egyptians, innumerable other nations. "If then I know not the meaning of the voice, I shall be to him that speaketh a barbarian." "For suppose not," saith he, "that this happens only in our case; rather in all one may see this taking place: so that I do not say this to disparage the voice, but to signify that to me it is useless, as long as it is not intelligible." Next, that he may not render the accusation unpalatable, he makes his charge alike for the two, saying, "He shall be unto me a barbarian, and I to him." Not from the nature of the voice, but from our ignorance. Seest thou how by little and little he draws men to that which is akin to the subject. Which is his use to do, to fetch his examples from afar, and to end with what more properly belongs to the matter. For having spoken of a pipe and harp, wherein is much that is inferior and unprofitable, he comes to the trumpet, a thing more useful; next, from that he proceeds to the very voice itself. So also before, when he was discounting to show that it was not forbidden the Apostles to receive, beginning first with husbandmen, and shepherds, and soldiers, then he brought the discourse on to that which is nearer to the subject, the priests in the old covenant. But do thou, I pray, consider, how every where he hath given diligence to free the gift from censure, and to bring round the charge to the receivers of it. For he said not, "I shall be a barbarian," but, "unto him that speaketh, a barbarian." And again, he did not say, "he that speaketh shall be a barbarian," but "he that speaketh shall be a barbarian unto me."

You see that the barbarian philosophy professes deeds, not words. The apostle thus speaks: "So likewise ye, except ye utter by the tongue a word easy to be understood, how shall ye know what is spoken? for ye shall speak into the air. There are, it may be, so many kind of voices in the world, and none of them is without signification. Therefore if I know not the meaning of the voice, I shall be unto him that speaketh a barbarian, and he that speaketh shall be a barbarian unto me."

If I do not understand the meaning of the words, then the speaker will seem to me a foreigner, that is, one speaking unintelligibly; and I will seem the same to him, not because of the poorness of the words, but because of our lack …

Here he shows their uselessness. And this is what he says: "If I have spoken in all tongues," but did not know the meaning of the words, I will be a foreigner to the speaker, and the speaker a foreigner to me. Note that barbarians …

For thus says the polite Ovid, when banished into Pontus, Barbarus hic ego sum, quia non intelligor ulli, I am a barbarian here, none understand me. To speak in the church in an unknown tongue is to talk gibberish; it is to play the barbarian; it is to confound the audience, instead of instructing them; and for this reason is utterly vain and unprofitable.