It is the last book in the Bible not because it was written last. Other New Testament books were written later. God put 65 books before Revelation, and you will never understand it until you have read all the other books. Almost every verse of the Revelation has a direct or implied reference to another part of the Bible. From those other parts you have the key to unlock the symbols and meaning in the Revelation.
Revelation means the unveiling, the drawing aside of the curtains.
He put away sin, defeated the devil, and rose again, carrying His Church into the heavenly places. Revelation is built on His finished work. In that sense, it unfolds history and interprets what is happening today in light of the end. Seven visions were given to John. Each begins with what Jesus did at the cross, interprets what is happening now because of that, and ends with His final coming.