The book
referred to here is the Revelation that Jesus told John to write down (Revelation 1:1, Revelation 1:10), which he did on a scroll. The sixty-six books that constitute our present Bible were not yet received by the churches as the definitive word of God (historically that took several more decades), and the technology required to print these sixty-six books between two covers as a single book (as we know books
) did not come into existence for another fifteen centuries. The scroll of the Revelation given to John contains revelation concerning a share in the tree of life and in the holy city.
19 and if anyone takes away from the words of the book of this prophecy, God will take away his share in the tree of life and in the holy city, which are described in this book.