A Letter to the Churches of Asia

The apostle has called his book a revelation (apocalypse) and a prophecy, but he puts it in the form of an epistle or letter. Notice that he begins in verse four and closes in the last verse of chapter 22 like an epistle:
John,

To the seven churches in the province of Asia:
Grace and peace to you from him who is, and who was, and who is to come, and from the seven spirits before his throne,
-- Rev 1:4 NIV

The grace of the Lord Jesus be with God's people. Amen.
-- Rev 22:21 NIV

If we compare those verses with the beginning and closing of Paul's epistle to the Philippians (Phil 1:1-2 and 4:13), we see that John's book is also an epistle. Since John's book is an epistle or letter, we should read it expecting the writer to discuss a situation faced by the churches at the time he wrote, and we should expect him to teach, encourage, and admonish the churches in a manner appropriate to that situation. In fact, we will find that John teaches as much about the work of Christ as Paul does in Romans, and he will apply that teaching to the situation faced by the churches of Asia in the late first century.