At that time priests were responsible for the rituals of temple worship and teaching the law of God. Prophets were responsible for listening to what God might be saying about Israel and other nations. They were often in conflict with one another. And the struggle between these two aspects of ministry has continued in the Christian Church for two thousand years. Priestly ministry is bound to be conservative and it should stick to the written word of God.
Prophetic ministry is unpredictable and unsettling.
Prophets announced the end of the northern kingdom by the Assyrians, and then the destruction of Jerusalem by the Babylonians. John the Baptist had to prepare the way for the coming of the Messiah, and was beheaded for doing so. The difference in the way God now began speaking through the new covenant prophets is striking. In the Old Testament period prophets were raised up for particular tasks in the nation. They had to point out the luxury, inhumanity, oppression, and military adventures of kings and nobles.