The Old Testament prophets were raised up by God to warn Israel of the promises of God regarding his judgment, when they turned away from him, and his forgiveness, when they returned to him. There message was continually fresh thus always contemporary. The prophets were placed at crisis points in Israel's history so they could address religious and social problems that plagued the people of the covenant. The theme(s) of the prophets seems to have included the following:
1. God rules in history.
2. God calls men and women to repentance.
3. All of society must be rooted in God's commandments.
4. Both judgment and hope are always the order of the day because God saves his people and judges his enemies.
5. The messianic kingdom describes a bright future state for all of those who trust God. It will come in God's time and way.
It was the seal of God's promises that he gave the prophets to Israel so that they could see what was far off and embrace it in true faith. The radiant glory that was to come would arrive in the person of the messiah. Finally, the apostles and prophets of the New Covenant clearly believed that the prophetic promises of the Old Testament were fulfilled in Jesus Christ. This is the whole point of scores of passages in the Gospels and epistles.
Jesus says that without the words of the prophets we cannot understand him (cf. Luke 24: 27, 32). In the light of this incredible claim I think we have the clearest reason of all for studying, and meditating in, the words of the prophets. We also have the clearest hermeneutic for how to apply these words to us and our time.