Obviously the Bible book of Revelation is what he means by “my revelations which I have caused to be written by my servant John.” These events are all part of the last days. The faithful can prepare by observing the multiple signs of the approaching end-times; but even more conclusively, the signs will confirm the truth of what was written.
Redaction: I suspect that the specificity of verse 16 is due to Joseph’s recognition that the book of Revelation fulfilled Moroni’s prophecy. It is doubtful that Moroni would have written so specifically, or in the past tense (“have caused to be written”).