John is commissioned to write to the seven churches of Asia (Revelation 1). He’s commissioned again as a prophet to prophesy (chapter 10).The reason is that his portfolio expands. He initially writes to the churches, and his visions have to do with the “land.” His second commission is to be prophet to “peoples, nations, tongues, king” (10:11).
It’s not the first time this happens. Elijah is re-commissioned when the dramatic show-down on Mount Carmel doesn’t stick (1 Kings 18-19). And when he’s recomissioned, he is given the charge to anoint a king of Aram (19:15), the first time an Israelite prophet has meddled so directly in Gentile politics.
It happens to Jonah too. He’s already a prophet when Yahweh orders him to prophesy in Nineveh.
Prophecy follows the general contours of God’s work in the world: To the Jew first, then to the Greek.