For he that speaketh in an unknown tongue - This verse is designed to show that the faculty of speaking intelligibly, and to the edification of the church, is of more value than the power of speaking a foreign language. The reason is, that however valuable may be the endowment in itself, and however important the truth which he may utter, yet it is as if he spoke to God only. No one could understand him.
Speaketh not unto men - Does not speak so that people can understand him. His address is really not made to people, that is, to the church. He might have this faculty without being able to speak to the edification of the church. It is possible that the power of speaking foreign languages and of prophesying were sometimes united in the same person; but it is evident that the apostle speaks of them as different endowments, and they probably were found usually in different individuals.
But unto God - It is as if he spoke to God. No one could understand him but God. This must evidently refer to the addresses “in the church,” when Christians only were present, or when those only were present who spoke the same language, and who were unacquainted with foreign tongues. Paul says that “there” that faculty would be valueless compared with the power of speaking in a manner that should edify the church. He did not undervalue the power of speaking foreign languages when foreigners were present, or when they went to preach to foreigners; see 1 Corinthians 14:22. It was only when it was needless, when all present spoke one language, that he speaks of it as of comparatively little value.
For no man understandeth him - That is, no man in the church, since they all spoke the same language, and that language was different from what was spoken by him who was endowed with the gift of tongues. As God only could know the import of what he said, it would be lost upon the church, and would be useless.
Howbeit in the Spirit - Although, by the aid of the Spirit, he should, in fact, deliver the most important and sublime truths. This would doubtless be the case, that those who were thus endowed would deliver most important truths, but they would be “lost” upon those who heard them, because they could not understand them. The phrase “in the Spirit,” evidently means “by the Holy Spirit,” that is, by his aid and influence. Though he should be “really” under the influence of the Holy Spirit, and though the important truth which he delivers should be imparted by his aid, yet all would be valueless unless it were understood by the church.
He speaketh mysteries - For the meaning of the word “mystery,” see Note, 1 Corinthians 2:7. The word here seems to be synonymous with sublime and elevated truth; truth that was not before known, and that might be of the utmost importance.