1 Corinthians 14:7-9

7Even in the case of lifeless instruments, such as the flute or harp, how will anyone recognize the tune they are playing unless the notes are distinct? 8Again, if the trumpet sounds a muffled call, who will prepare for battle? 9So 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.