I Peter 1:13, "Wherefore gird up the loins of your mind, be sober, and hope to the end for the grace that is to be brought unto you at the revelation of Jesus Christ."
 

The word revelation means "an unveiling." In Greek it is the word apokalupsis {ap-ok-al'-oop-sis}. The definition in Strong's Concordance is: 1) laying bear, making naked 2) a disclosure of truth, instruction 2a) concerning things before unknown 2b) used of events by which things or states or persons hitherto withdrawn from view are made visible to all 3) manifestation, appearance. It is as though we draw the curtain back revealing what is behind it.

In 95 A.D., while the apostle John was in exile on the island of Patmos, God drew the curtain back revealing to him those things which are and those things which must shortly come to pass.  

Ephesians 1:17-22, "That the God of our Lord Jesus Christ, the Father of glory, may give unto you the spirit of wisdom and revelation in the knowledge of him: The eyes of your understanding being enlightened; that ye may know what is the hope of his calling, and what the riches of the glory of his inheritance in the saints, And what is the exceeding greatness of his power to us-ward who believe, according to the working of his mighty power, Which he wrought in Christ, when he raised him from the dead, and set him at his own right hand in the heavenly places, Far above all principality, and power, and might, and dominion, and every name that is named, not only in this world, but also in that which is to come: And hath put all things under his feet, and gave him to be the head over all things to the church, Which is his body, the fullness of him that filleth all in all."

The book of Revelation gives us insight into those things which John saw, those things which are, and those things which will come to pass.