The angel provides the answer: I am a fellow servant with you.
Before God, this angel is on the same level as John himself, that is, equally a servant (= slave), obligated to do the Master’s bidding. In this case he was simply the obedient bearer of God’s message.
9 but he said to me, “You must not do that! I am a fellow servant with you and your brothers the prophets, and with those who keep the words of this book. Worship God.”