The revelation of Jesus Christ, which God gave him to show his servants what must soon take place. He made it known by sending his angel to his servant John, who testifies to everything he saw—that is, the word of God and the testimony of Jesus Christ.  Revelation 1:1-2

The word “Revelation” – or in the Greek, apokalypsis – means revealing what was unknown, disclosing of a truth.  It was revealing something that was once unknown.

Jesus wanted to reveal that an event will SOON take place.  The Greek word for soon is tachos which means quickness, speed.  It's the same “soon” used at the end in Revelation 22:6.  A similar word emphasizes the urgency of this statement.

Blessed is the one who reads the words of this prophecy, and blessed are those who hear it and take to heart what is written in it, because the time is near.  Revelation 1:3

The time is NEAR.  Near and soon.  What event could be happening near and soon to the time of John.

While many argue the date of the writing of John, these two words at the opening make the strongest case that it was written before 70 AD, when Rome destroyed the Temple and leveled Jerusalem, killing, as Josephus said, nearly one million people.  That's a huge catastrophe to our standards today.

Wouldn't that be an event that God would want to warn them about in their near future?