Paul points out
A. The uselessness of anything that makes an uncertain sound.
1 Corinthians 14:7-11 (KJV)
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.
Therefore if I know not the meaning of the voice, I shall be unto him that speaketh a barbarian, and he that speaketh shall be a barbarian unto me.

B. Some people today say that they use tongues to "pray in the spirit."
1 Corinthians 14:12-17 (KJV)
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?
For thou verily givest thanks well, but the other is not edified.

C. Paul was thankful for his gift of tongues.
1 Corinthians 14:18-19 (KJV)
I thank my God, I speak with tongues more than ye all:
Yet in the church I had rather speak five words with my understanding, that by my voice I might teach others also, than ten thousand words in an unknown tongue.

The Bible never once tells of Paul using a supernatural ability to speak a language he did not know.

We do know, however, that he spoke several foreign languages.
• Hebrew
• Greek (Acts 21:37), probably
• Aramaic , and perhaps even
• Latin
I am sure that, being a traveling church planter as he was, speaking all these languages was useful. But, he said, even then he would not use them in the church.