1 Corinthians 14:11 (KJV)

Now, brethren, if I come unto you speaking with tongues, what shall I profit you, except I shall speak to you either by revelation, or by knowledge, or by prophesying, or by doctrine?

And even things without life giving sound, whether pipe or harp, except they give a distinction in the sounds, how shall it be known what is piped or harped?

For if the trumpet give an uncertain sound, who shall prepare himself to the battle?

So likewise ye, except ye utter by the tongue words easy to be understood, how shall it be known what is spoken? for ye shall speak into the air.

There are, it may be, so many kinds of voices in the world, and none of them is without signification.

Even so ye, forasmuch as ye are zealous of spiritual gifts, seek that ye may excel to the edifying of the church.

Wherefore let him that speaketh in an unknown tongue pray that he may interpret.

For if I pray in an unknown tongue, my spirit prayeth, but my understanding is unfruitful.

What is it then? I will pray with the spirit, and I will pray with the understanding also: I will sing with the spirit, and I will sing with the understanding also.

Else when thou shalt bless with the spirit, how shall he that occupieth the room of the unlearned say Amen at thy giving of thanks, seeing he understandeth not what thou sayest?