Revelation 1:9 I John, who also am your brother, and companion in tribulation, and in the kingdom and patience of Jesus Christ, was in the isle that is called Patmos, for the word of God, and for the testimony of Jesus Christ.
The word of God is the scriptures and more specifically the gospel preached by Jesus and his apostles.
Acts 4:31 And when they had prayed, the place was shaken where they were assembled together; and they were all filled with the Holy Spirit, and they spake the word of God with boldness.
John had been exiled on the isle of Patmos for preaching the gospel – the word of God and the testimony of Jesus Christ – that is – the gospel.
On the isle of Patmos, he receives a series of visions which he writes down as the Revelation of Jesus Christ.
The visions comprise a prophecy in symbolic form of the future events in the world from the end of the first century AD, through to the millennial reign of Jesus Christ upon the earth, followed by the final resurrection and judgment to the fulfilment of the purpose of God. The time when sin and death will be eradicated, and God will live in and with his creation and be ‘all in all’.
1 Corinthians 15:28 And when all things shall be subdued unto him, then shall the Son also himself be subject unto him that put all things under him, that God may be all in all.
Revelation 21:3 And I heard a great voice out of heaven saying, Behold, the tabernacle of God is with men, and he will dwell with them, and they shall be his people, and God himself shall be with them, and be their God. 4 And God shall wipe away all tears from their eyes; and there shall be no more death, neither sorrow, nor crying, neither shall there be any more pain: for the former things are passed away.
I hope you find this helpful.