What does Revelation 22:8 mean?

This is another curious instance were John seemingly does something foolish by attempting to worship an angel (Revelation 19:10). Whether this was a matter of mistaken identity, or simple error, the angel is quick to correct John's mistake (Revelation 22:9). John knew that the first commandment forbade the worship of anyone or anything but God. He should have realized—or remembered—that worshiping an angel is sin. However, whether out of shock, confusion, or simply an overwhelmed spirit, he was ready to worship the angel who showed him scenes in Revelation. One possible explanation is that John mistook the words of verse 7 as coming from the angel: he might have thought "I am coming soon" meant that Jesus had taken the form of that being while speaking to John.

Authors seldom disclose their faults—especially when they're inventing stories. Yet John admitted this mistake, adding credibility to his writing. Biblical authors, like John, wrote about their sins in spite of risking a lower opinion of themselves. For example, Moses admitted that he was reluctant to represent God before Pharaoh. He claimed he could not speak, and he asked God to send someone else (Exodus 4:10–13). King David committed his sins of adultery and murder, but, after covering them for a while, he wrote about those sins and confessed them to God (2 Samuel 11:2–27; Psalm 51). It is evidence of biblical inspiration that the authors of inspired Scripture laid bare their sins.