1-corinthians 14:9

Likewise ye - If ye do not speak in the Church so as to be understood, your labor is useless; ye shall speak into the air - your speech will be lost and dissipated in the air, without conveying any meaning to any person: there will be a noise or sound, but nothing else. Gifts of that kind, thus used, are good for nothing.

So likewise ye ... - To apply the case. If you use a foreign language, how shall it be known what is said, or of what use will it be, unless it is made intelligible by interpretation?

Utter by the tongue - Unless you speak.

Words easy to be understood - Significant words (margin), words to which your auditors are accustomed.

For ye shall speak into the air - You will not speak so as to be understood; and it will be just the same as if no one was present, and you spoke to the air. We have a proverb that resembles this: "You may as well speak to the winds:" that is, you speak where it would not be understood, or where the words would have no effect. It may he observed here, that the practice of the papists accords with what the apostle here condemns, where worship is conducted in a language not understood by the people; and that there is much of this same kind of speaking now, where unintelligible terms are used, or words are employed that are above the comprehension of the people; or where doctrines are discussed which are unintelligible, and which are regarded by them without interest. All preaching should be plain, simple, perspicuous, and adapted to the capacity of the hearers.

14:9 Unless ye utter by the tongue - Which is miraculously given you. Words easy to be understood - By your hearers. Ye will speak to the air - A proverbial expression. Will utterly lose your labour.