If any man think himself to be a prophet, or spiritual, let him acknowledge that the things that I write unto you are the commandments of the Lord.
Prophet - the species.
Spiritual - the genus: spiritually endowed. The followers of Apollos prided themselves as "spiritual" (1 Corinthians 3:1-3). Here one capable of discerning spirits is specially meant.
Things that I write ... commandments of the Lord, ('Aleph (') A B C read the singular, referring to the last commandment alone; namely, that women should be silent in church-`that it is the commandment of the Lord.' The Vulgate supports the Received Text) - a direct assertion of inspiration. Paul's words are Christ's words. Paul appeals not merely to one or two, but to a body of men, for the reality of three facts about which no body could be mistaken:
(1) That his influence over them was not due to mere eloquence, but to the "demonstration of the Spirit and of power;"
(2) That part of this demonstration consisted in imparting miraculous gifts which they were then exercising so generally as to require to be corrected in the irregular employment of them;
(3) That among these was one which enabled the "prophet" or 'spiritual person,' to decide whether Paul's letter was Scripture or not.
He could not have written so unless the facts were notoriously true; for he takes them for granted, as consciously known by the whole body of men whom he addresses (Hinds, 'On Inspiration').