John explains that he was on the island on account of the word of God and the testimony of Jesus.
These words are open to multiple understandings:
John was banished to this island because of hostility to his work as preacher of the gospel. In this understanding the island served as a prison.
John was on Patmos with a view to receiving Jesus’ revelation.
John was on Patmos as a missionary in order to preach the gospel to the inhabitants.
Without excluding the obvious reality of points 2 and 3, the most convincing explanation for John’s presence on the island is point 1. That’s because persecution on account of the faith appears numerous times in Revelation (Revelation 6:9; Revelation 20:4), and John’s personal involvement in persecution is certainly hinted at in the terms tribulation
and patient endurance
earlier in Revelation 1:9. We might add that writings from the early church (not so many years after John received this Revelation) indicate that John was indeed on the island as a prisoner of the state.
9 I, John, your brother and partner in the tribulation and the kingdom and the patient endurance that are in Jesus, was on the island called Patmos on account of the word of God and the testimony of Jesus.