"The art prophecy is very difficult," Mark Twain once said, "especially with respect to the future." Surprisingly, Twain's words pretty much describe biblical prophecy.
In the vast majority of cases, the biblical prophets were not in the business of predicting the future--that idea came along much later in the history of prophecy--but of saying something important about the present, though sometimes in terms of the future. Prophet doesn't mean one who predicts what is to come but refers to the Greek word prophetes: "one who speaks for another."
In Hebrew scripture prophets spoke for God. Their visions, revelations, and other intense mystical experiences gave them a certain standing and authority to defend God in their day and bring the people--kings included--to task for superstitious beliefs, idolatry, and moral failings. Prophets brought and interpreted the word of God to a people who needed to be reminded of it.
Most of the discussion of prophecy in the New Testament comes from St. Paul, though prophets show up in the Acts of the Apostles, which calls some of them people who "encourage and strengthen the believers" (Acts 15:32). In the gospels John the Baptist was "regarded ... as a prophet" (Matt. 14:5), and the travelers on the road to Emmaus called Jesus a "prophet mighty in deed and word before God and all the people" (Luke 24:19). …