‘Blessed is he who reads, and they who hear the words of the prophecy, and keep the things which are written in it, for the time is at hand.'
The book was intended to be read to churches and a special blessing is promised to the one who does the reading and to those who receive its message and respond to it. Books to be read in church were those which were seen as the inspired word of God (later a clear distinction would certainly be made between books to be read in the churches because they were accepted as the word of God and those which could be read as spiritually useful but not the word of God). Thus John is claiming that this is the inspired word of God.
‘For the time is at hand.' It is not a book just about the distant future. It is writing about something of imminent concern for the churches. It has present relevance for them, and its events will apply to their times and their lives.
John begins by describing the source of his revelation.