1 Corinthians 14:6-13

Now, brothers and sisters, if I come to you and speak in tongues, what good will I be to you, unless I bring you some revelation or knowledge or prophecy or word of instruction? Even in the case of lifeless things that make sounds, such as the pipe or harp, how will anyone know what tune is being played unless there is a distinction in the notes? Again, if the trumpet does not sound a clear call, who will get ready for battle? So it is with you. Unless you speak intelligible words with your tongue, how will anyone know what you are saying? You will just be speaking into the air. Undoubtedly there are all sorts of languages in the world, yet none of them is without meaning. If then I do not grasp the meaning of what someone is saying, I am a foreigner to the speaker, and the speaker is a foreigner to me. So it is with you. Since you are eager for gifts of the Spirit, try to excel in those that build up the church. For this reason the one who speaks in a tongue should pray that they may interpret what they say.