1 Corinthians 14:9
King James Version
“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.”
Context
6Now, 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?
7And 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?
8For if the trumpet give an uncertain sound, who shall prepare himself to the battle?
9So 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.
10There are, it may be, so many kinds of voices in the world, and none of them without signification.
11Therefore if I know not the meaning of the voice, I shall be unto him that speaketh a barbarian, and he that speaketh a barbarian unto me.
12Even so ye, forasmuch as ye are zealous of spiritual seek that ye may excel to the edifying of the church.