Thematic Bible: Of foreign tongues

So also you, unless you utter by the tongue speech that is clear, how will it be known what is spoken? For you will be speaking into the air. There are, perhaps, a great many kinds of languages in the world, and no kind is without meaning. If then I do not know the meaning of the language, I will be to the one who speaks a barbarian, and the one who speaks will be a barbarian to me. read more.
So also you, since you are zealous of spiritual gifts, seek to abound for the edification of the church. Therefore let one who speaks in a tongue pray that he may interpret. For if I pray in a tongue, my spirit prays, but my mind is unfruitful. What is the outcome then? I will pray with the spirit and I will pray with the mind also; I will sing with the spirit and I will sing with the mind also. Otherwise if you bless in the spirit only, how will the one who fills the place of the ungifted say the "Amen" at your giving of thanks, since he does not know what you are saying? For you are giving thanks well enough, but the other person is not edified. I thank God, I speak in tongues more than you all; however, in the church I desire to speak five words with my mind so that I may instruct others also, rather than ten thousand words in a tongue.