1 Co 14:14.

For if I pray in an unknown tongue, my spirit prayeth, but my understanding is unfruitful. 

1 Co 14:14.

Whereas speaking with tongues is of profit only for the one who speaks (→ I, 722, 15 f.), the prophet edifies the whole community. The prophet’s message is for all the members, while the man who speaks with tongues speaks to God and does not profit the whole body, 1 C. 14:2 f. It is true that human volition is not ruled out in the case of the man who speaks with tongues. When Paul himself does this, he is master of his actions, 1 C. 14:19. The man who speaks with tongues does not have to speak if he does not want, so that the number of those who speak with tongues at divine service may be fixed, 1 C. 14:27. But the understanding has no part (1 C. 14:14), and to those outside the man who speaks with tongues seems like a maniac, 1 C. 14:23 → IV, 959, 7 ff. Prophecy, on the other hand, is intelligible speech. The spiritual experience is worked out and presented by the prophet in intelligible form, so that what is said may be understood by all, including outsiders as well as members, 1 C. 14:24 f. → V, 141, 21 ff.

Gerhard Friedrich, “Προφήτης, Προφῆτις, Προφητεύω, Προφητεία, Προφητικός, Ψευδοπροφήτης,” ed. Gerhard Kittel, Geoffrey W. Bromiley, and Gerhard Friedrich, Theological Dictionary of the New Testament (Grand Rapids, MI: Eerdmans, 1964–), 852.