In Revelation 10, John is instructed to eat a small scroll, which tastes sweet but causes bitterness, symbolizing the dual nature of prophecy. A mighty messenger from God appears, holding the scroll and declaring a universal authority over land and sea, while his message highlights both mercy and impending judgment. John is commanded to prophesy about the coming events, emphasizing the fulfillment of God's plan, the completion of the mystery, and the eventual destruction of Jerusalem.