It is the misunderstanding of this verse which, we believe, has led so many astray, and turned so many into the wrong channel. This verse is usually taken as referring to three things, marking off the book into three divisions:
The things which thou sawest (past). The things which are (present). The things which shall be hereafter (future).
Having got these three divisions, then comes a difference of opinion as to exactly where and how these contents of the Book are to be divided.
But there is another rendering which we wish to present, suggested, in part, by Moses Stuart and Dean Alford. This removes all such difficulties, and shows that there is no such three-fold division; and that instead of three subjects we have only one.
John was instructed to write what he had seen. It is clear, therefore, that this first chapter is the Introduction to the whole Book, and consequently, like all other Introductions, is written, or supposed to be written, last of all. For, at the very commencement (in i.2), it is said of John that he "bare record of the Word of God (i.e., as we have seen, the prophetic message), and of the testimony of Jesus Christ (which He bore) and of all things that he saw."
If this chapter then be not written after John had see these things, the words are without meaning; for in that case John had as yet seen nothing!
Verse 19 (which we are considering) is part of this Introduction, and therefore the words "which thou sawest" are used in the same sense as in verse 2. John had seen, or is supposed to have seen, all the Visions of the Book when the command to write was given to him. This explains why the word "therefore" must be added in the Greek (according to all the Critical Greek Texts and the R.V.). Moreover, it is specially declared at the very end of the book (chap. xxii.16), "I Jesus have sent mine angel to testify unto THESE THINGS in the assemblies": showing that "the things which thou sawest" refer, not as is generally supposed, only to the things in chap. i., but to the contents of the whole book.
Having seen all these things the command is - "Write therefore the things which thou sawest, and what they are (i.e., what they signify),  even the things which shall come to pass (i.e., happen, as in Acts xxvi.22) hereafter."
According to this rendering, which may be rejected as an interpretation, but cannot be condemned as a translation, there is only one thing stated as the subject-matter of what was to be written, and not three things. It relates not to past, present, and future, but to the future alone - "hereafter," or, as it says in Dan. xi.14, "in the latter days."
Some lay a stress on the words (...), meta tauta, which mean literally after these things. But an examination of other places where they occur will show that when used in narrative they may imply historical sequence (as in Luke v.27; x.1; xii.4; xvii.8; xviii.4. John iii.22; v.14; vii.1; xix.38; xii.1. Acts xiii.20; xviii.1); yet when used in connection with promise or prophecy, they, as naturally, are indefinite, hereafter. (John xiii.7. Acts vii.7.1 Peter i.1, where it is rendered "should follow," and has not followed even yet). In any case, the A.V. and R.V. both render the expression "hereafter" where it occurs in Revelation, viz., i.19; iv.1; and ix.12, in a prophetic sense.
There is no necessity therefore for anyone to regard any portion of the book as relating to the present church period. This (in which we live) is the Dispensation of the Holy Spirit; but that (which is the subject of the Revelation) is wholly the Dispensation of the Son of Man - the revelation or unveiling and manifestation of Jesus Christ.
That is still future. The book which describes it must likewise be future also, and relate only to "the things which shall be hereafter." See further notes on chap. i.19.
 As to this rendering, "and what they ARE," the verb to be is constantly translated to mean or signify. See Matthew 9:13: "But go ye and learn what that IS" (A.V. and R.V. meaneth). Matthew 12:7: "but if ye had known what that IS" (A.V. and R.V. meaneth). Luke 15:26: "He asked what these things WERE" (A.V. meant; R.V. might be). Acts 2:12: "What IS this?" (A.V. and R.V. What meaneth this). Acts 10:17: "Now, while Peter doubted in himself what this vision WAS which he had seen" (A.V. What this vision should mean; R.V. might mean). So, "and what they ARE" should be rendered "and what they mean," or signify.