1 Corinthians 14:7-13

If even lifeless instruments, such as the flute or the harp, do not give distinct notes, how will anyone know what is played? And if the bugle gives an indistinct sound, who will get ready for battle? So with yourselves, if with your tongue you utter speech that is not intelligible, how will anyone know what is said? For you will be speaking into the air. There are doubtless many different languages in the world, and none is without meaning, but if I do not know the meaning of the language, I will be a foreigner to the speaker and the speaker a foreigner to me. So with yourselves, since you are eager for manifestations of the Spirit, strive to excel in building up the church. Therefore, one who speaks in a tongue should pray that he may interpret.