2 For he that speaketh in an unknown tongue speaketh not unto men, but unto God: for no man understandeth understandeth: Gr. heareth him; howbeit in the spirit he speaketh mysteries.
English Standard Version
2 For one who speaks in a tongue speaks not to men but to God; for no one understands him, but he utters mysteries in the Spirit.
2 If you praise him in the private language of tongues, God understands you but no one else does, for you are sharing intimacies just between you and him.
New King James Version
2 For he who speaks in a tongue does not speak to men but to God, for no one understands him; however, in the spirit he speaks mysteries.
New Living Translation
2 For if you have the ability to speak in tongues, you will be talking only to God, since people won't be able to understand you. You will be speaking by the power of the Spirit, but it will all be mysterious.
Prophesying, that is, explaining Scripture, is compared with speaking with tongues. This drew attention, more than the plain interpretation of Scripture; it gratified pride more, but promoted the purposes of Christian charity less; it would not equally do good to the souls of men. What cannot be understood, never can edify. No advantage can be reaped from the most excellent discourses, if delivered in language such as the hearers cannot speak or understand. Every ability or possession is valuable in proportion to its usefulness. Even fervent, spiritual affection must be governed by the exercise of the understanding, else men will disgrace the truths they profess to promote.