A voice commands John to approach the angel to ask for the scroll. The angel gives him the little scroll with the command that he should eat it. John obeys the angel and eats the entire scroll. It was rather easy to eat the small scroll since it was sweet in his mouth, but it was difficult to hold it in his body since it had become bitter in his stomach.
Centuries back, prophet Ezekiel had a similar experience at the beginning of his prophetic career (Ezek 3:1-3). Just as Ezekiel was told, John was also told that, 'you must again prophesy about many peoples and nations and languages and kings' (Rev 10:11). Eating the scroll was to prepare him to preach to the nations and their rulers.
Now, to unpack the symbolism. What is this scroll and what is the purpose of eating it? We are told that the scroll is open. Anyone who has been following the sequence of events in the Book of Revelation so far might have noticed that the Lamb (risen Lord) has already opened it (Rev 6:1). The image of the angel coming down from heaven with the scroll is the symbolic representation of the truth that we find in (Hebrews 2:2). According to some Jewish interpretation of the event where Moses received the Law, the revelation of God was handed down to him through angels.
John has to eat what God has revealed through the son and given to him now. This eating is thus the preparation for the mission to the nations and their rulers. It is a bittersweet reality. The word of God is sweeter than the honey, however, bringing it out is most of the time a bitter reality. What you like and cherish may not always in line with people out there like to cherish. This brings God's people in conflict with others. However, it has to be done! But before that is done, we need to really grasp the word thoroughly like we eat something so that it becomes part of our body system.