1 Corinthians 14:8-10

Amplified Bible

⁸ And if the [war] bugle produces an indistinct sound, who will prepare himself for battle? ⁹ So it is with you, if you speak words [in an unknown tongue] that are not intelligible and clear, how will anyone understand what you are saying? You will be talking into the air [wasting your breath]! ¹⁰ There are, I suppose, a great many kinds of languages in the world [unknown to us], and none is lacking in meaning.