But now, brethren, if I come to you speaking with tongues, what shall I profit you unless I speak to you either by revelation, by knowledge, by prophesying, or by teaching? 7 Even things without life, whether flute or harp, when they make a sound, unless they make a distinction in the sounds, how will it be known what is piped or played? 8 For if the trumpet makes an uncertain sound, who will prepare for battle? 9 So likewise you, unless you utter by the tongue words easy to understand, how will it be known what is spoken? For you will be speaking into the air. 10 There are, it may be, so many kinds of languages in the world, and none of them is without significance. 11 Therefore, if I do not know the meaning of the language, I shall be a foreigner to him who speaks, and he who speaks will be a foreigner to me. 12 Even so you, since you are zealous for spiritual gifts, let it be for the edification of the church that you seek to excel.
13 Therefore let him who speaks in a tongue pray that he may interpret. 14 For if I pray in a tongue, my spirit prays, but my understanding is unfruitful. 15 What is the conclusion then? I will pray with the spirit, and I will also pray with the understanding. I will sing with the spirit, and I will also sing with the understanding. 16 Otherwise, if you bless with the spirit, how will he who occupies the place of the uninformed say “Amen” at your giving of thanks, since he does not understand what you say? 17 For you indeed give thanks well, but the other is not edified.
18 I thank my God I speak with tongues more than you all; 19 yet in the church I would rather speak five words with my understanding, that I may teach others also, than ten thousand words in a tongue.
— 1 Corinthians 14:6-19.
In using their gift of tongues [speaking in unlearned languages], interpretation must be given. Paul emphasizes the need to be clearly understood by one’s hearers.