1 Corinthians 14:9-11

So also ye, unless ye utter by the tongue speech easy to be understood, how shall it be known what is spoken? for ye will be speaking into the air. There are, it may be, so many kinds of voices in the world, and no kind is without signification. If then I know not the meaning of the voice, I shall be to him that speaketh a barbarian, and he that speaketh will be a barbarian unto me.