Revelation 1:19

19 Write the things which thou hast seen, and the things which are, and the things which shall be hereafter;

This is a key verse because it sets the parameters for the entire book.   John is the representative chosen to become a time traveler and see Jesus revealed in his Church through time through the working of His Holy Spirit in the Church. John will actually go through the same experiences the Church does through time. The inference in the Gospel of John that many thought John would not die until he experienced the coming of the kingdom makes a little more sense if the disciples were led to believe through the teaching of Jesus that John would experience it in his lifetime.

John 21:22 Jesus saith unto him, If I will that he tarry till I come, what is that to thee? follow thou me.

Jesus told John:

Write what thou  saw - Chapter one of this book - John sees the glorified Son of God. John also sees the candlesticks in Revelation 1:20 that have Jesus in their midst. The candlesticks we are told in verse 20 represent the Church. John in verse 17 then acts out what each person must do to become part of this assembly that will be with Jesus. He dies at the feet of Jesus and is resurrected by the right hand of God and raised to new life by the indwelling presence of His Holy Spirit.

Write what things  are - Chapter s two and three of this book - John as a member of the Church describes what is going on in the entire age of the new covenant Church on earth and what the specific message of Jesus is to each member identified with one of these seven church types or church ages. These seven churches represent the primary attributes and the works to be found in the Church through time during the New Covenant Church age on earth. John is going forward in time to the day when Jesus comes for His Church so the message and the works in the seven letters are sequential in time.

Write what will be  hereafter - Chapter four through the rest of the book - John goes to heaven with the faithful Church at the great snatching away of this Church (known as the rapture). John sees the events that happen in heaven and on earth after the church age on earth. Any prophecies in this book that start with events prior to the rapture of chapter four have John looking back in time from the Rapture.