This verse describes a prophet's major responsibility, but here and there in the Bible a prophet is called a "watchman" or "man of God." They are also described as pastors. Whatever they are called, there is always some indication that they were set apart from the normal system, even if they happened to be Levitical priests. Jeremiah and Ezekiel were both priests, but they were not part of the system, standing apart from it despite being of Aaron's family. What God did in setting them apart made them recognizable to the people as "a man of God," as a "watchman."
Although the biblical record appears to show gaps between prophetic activities, it is probable that, until the New Testament times, there were always prophets among the people. The last Old Testament prophet was John the Baptist, who, although appearing in the New Testament, was still operating under the Old Covenant. His father, Zechariah, was a priest, and even though John came from a priestly family, he was definitely different from the priests of his day. In fact, he stood out like a sore thumb. This standing apart is always an identifying mark of a prophet. Though a prophet may be a priest, he is definitely not part of the priesthood system.
The prophets whose writings make up much of the biblical record tend to appear just before a time of crisis or during the crisis itself. Sometimes they were well organized, as in Samuel's or Elijah's day, when schools of the prophets existed. However, these schools tended to produce - not prophets in the classic sense like Samuel, Jeremiah, Ezekiel, or Isaiah - but the equivalent of modern-day theological seminarians. We can speculate that they were probably mostly Levites, who, as part of their Tabernacle/Temple service or priesthood training, attended these schools. Undoubtedly, some of these spoke under the inspiration of God, but they were not prophets in the same sense as the well-known prophets of Scripture.
Sometimes a prophet's ministry was accompanied by tremendous miracles, as with Elijah and Elisha. God used these signs and wonders to reinforce their ministry. At other times, as with John the Baptist, no miracles at all were performed (John 10:41). In other words, no one pattern emerges on this point. The chief distinction is that they were men set apart.
John W. Ritenbaugh
Prophets and Prophecy (Part 1)