9 So also you, unless you uttered by the tongue words easy to understand, how would it be known what is spoken? For you would be speaking into the air. 10 There are, it may be, so many kinds of sounds in the world, and none of them is without meaning. 11 If then I don’t know the meaning of the sound, I would be to him who speaks a foreigner, and he who speaks would be a foreigner to me. 12 So also you, since you are zealous for spiritual gifts, seek that you may abound to the building up of the assembly. 13 Therefore let him who speaks in another language pray that he may interpret.
Matthew Henry's Commentary on 1 Corinthians 14:9-13
Commentary on 1 Corinthians 14:6-14
(Read 1 Corinthians 14:6-14)
Even an apostle could not edify, unless he spoke so as to be understood by his hearers. To speak words that have no meaning to those who hear them, is but speaking into the air. That cannot answer the end of speaking, which has no meaning; in this case, speaker and hearers are barbarians to each other. All religious services should be so performed in Christian assemblies, that all may join in, and profit by them. Language plain and easy to be understood, is the most proper for public worship, and other religious exercises. Every true follower of Christ will rather desire to do good to others, than to get a name for learning or fine speaking.