A Divine Table of Contents
Commentators widely see this verse as Christ providing a three-part outline for the book of Revelation. John is to write: 1) 'the things which thou sawest' (the vision of Christ in chapter 1), 2) 'the things which are' (the state of the seven churches in chapters 2-3), and 3) 'the things which shall be hereafter' (the prophetic visions from chapter 4 onward). This serves as a divine table of contents for the reader.