Most of the book can be understood and that which cannot be understood and believed should simply be believed, just as we believe the Trinity, though we cannot explain it. For this reason the study of Revelation is really the study of the whole rest of the Bible. The first word in the original is Apocalypse which indicates that this is a revelation of information to man, by God, which man could know in no other way. Apocalypse translates into English as Revelation , hence the name of the book. Past history is difficult enough to see and understand rightly.
Future history is even more difficult to see when explained in advance.
Thus the difficulty of the book. Scripture interprets Scripture. The complete agreement of Scripture with itself, must be accepted by faith as a basis of interpretation. The meaning of words in Scripture must be understood and explained in accordance with their use in the spoken and written language of their day. The explanation must be grammatico-historically correct.