3 But when you proclaim his truth in everyday speech, you're letting others in on the truth so that they can grow and be strong and experience his presence with you. 4 The one who prays using a private "prayer language" certainly gets a lot out of it, but proclaiming God's truth to the church in its common language brings the whole church into growth and strength.
Matthew Henry's Commentary on 1 Corinthians 14:3-4
Commentary on 1 Corinthians 14:1-5
(Read 1 Corinthians 14:1-5)
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.