A key to the two-part nature of the Book is found in chapter 10, verse 11:
You must prophesy again about many peoples, nations, languages and kings.
After the letters to the seven churches, there are two great sections to the Book:
Section One: The First Enemy of the Church and its destruction.
Section Two: The Second Enemy of the Church and its destruction.
This verse stands between them.
If the second section deals with all sorts of peoples of various languages (hint, hint), what do you think the first section deals with?
Just a few thoughts to get you searching. Have fun!