The book of Revelation is the revelation of Jesus Christ
John was writing to the seven churches in Asia (that existed then)
1 The Revelation of Jesus Christ, which God gave unto him, to shew unto His servants things which must shortly come to pass; and he sent and signified it by his angel unto his servant John:
2 Who bare record of the word of God, and of the testimony of Jesus Christ, and of all things that he saw.
3 Blessed is he that readeth, and they that hear the words of this prophecy, and keep those things which are written therein: for the time is at hand.
John to the seven churches which are in Asia: Grace be unto you, and peace, from him which is, and which was, and which is to come; and from the seven Spirits which are before His throne;