"He had come like a thief in the night." is taken from the Bible, specifically Thessalonians 5:2. It refers to the second return of the Lord (Jesus), that means another one from the one we know. The first one is his rebirth after beeg crucified. He will return as "a thief in the night" because we don't know when it will happen, he won't announce it.
The author is giving details and purpose to this event and is inviting people to come to attend it. They even tell you how you can get to the event and about the designated "drop zones".
