Our English understanding of the word "prophet" usually includes some idea of predicting the future -- and we'll judge a prophet by his or her accuracy in forecasting. There's nothing wrong with this definition, although it sometimes leaves us switching between "prophet" and "National Enquirer psychic" a little too easily.
But when we study prophecy in the Bible, we should remember that the word we translated as prophet wasn't just about predicting the future. In fact, that was really a small part of a prophet's role. The na'vi, which is the Hebrew word we translate prophet, was thought of as a special kind of spokesperson for God. In old gangster movies, the criminals wouldn't talk to anyone until their "mouthpiece" or lawyer was present. A na'vi was that kind of "mouthpiece."
So a prophet's message is not just the prophet's message -- it's God's message, delivered through a human mediator. Even when prophecy in the Old Testament focused more on pointing out what was going wrong than what was going to happen in the future, the prophets would say that their ability to discern and see patterns in the events of the day came from God.
Prophets were also less concerned with predicting what was going to happen than they were with warning what was going to happen unless. The Old Testament prophets warned the people of Israel and Judah that their mixing idol worship into their daily lives meant that when the time came to rely on God, they would be lost because they wouldn't know how to do that anymore. And they warned them that a failure to live as God's people would come back to haunt them if the time came when they were under another nation's laws that made no allowance for God's law.
In other words, the prophet's message is most often a warning and offers guidance. The opening part of the book of Revelation does just this for the seven churches mentioned in this passage. Jesus, speaking to John in a vision, warns these churches of the dangers each of them faces and tries to guide them past those dangers. A church that has lost its passion is encouraged to try to recapture it. A church that seems to be going through the motions, neither hot nor cold, is encouraged to take a stand and make a difference, and so on.
Prophets' words do this for churches, communities of people, and for individuals as well. John wrote down what he saw because Jesus told him to, not just to speak to me. But his words do speak to me, to guide me away from the dangers I might face in my walk with Christ and to point out what those dangers are. I am encouraged to recapture my early passion for following Jesus. I am encouraged to make a stand rather than try to have something both ways. I am warned that if I depend on something other than God, I might have more trouble because I may forget how to depend on God.
Interestingly, the second part of Revelation -- the part with the really wild stuff in it and the part that some people have chosen to use to try to scare people into their way of thinking -- is actually the part that's supposed to give hope to people facing the problems outlined in the first part! It's "apocalyptic" message wants its readers to understand that God wins in the end, and that even though they may have failed, God offers lasting forgiveness and redemption.
The prophet's message is: "Watch out, God is coming." The apocalypticist's message is, "Hold on, God is coming." Both, of course, are needed.