1 Corinthians 14:9-11

14:9 It is the same for you. If you do not speak clearly with your tongue, how will anyone know what is being said? For you will be speaking into the air. 14:10 There are probably many kinds of languages in the world, and none is without meaning. 14:11 If then I do not know the meaning of a language, I will be a foreigner to the speaker and the speaker a foreigner to me.