It is not easy to confront a person (let alone a whole church) about his use of spiritual gifts. Paul shows great pastoral sensitivity as he does this, calling his readers his brothers
and offering himself as an example. He asks the Corinthians to imagine what they would have thought if he had come to them speaking in tongues, instead of communicating an intelligible message.
The fact is that whenever Paul addressed the church, it was always with some revelation or knowledge or prophecy or teaching.
These four words form two complementing pairs. Revelation (knowledge that comes directly from God) is given to a person in order to share it with the church as a prophecy. Knowledge (in this context, probably the knowledge of previously revealed truth) is given to someone in order to transmit it to the church as a teaching.
6 Now, brothers, if I come to you speaking in tongues, how will I benefit you unless I bring you some revelation or knowledge or prophecy or teaching?