I used to think that a lot of Luke 21 was about the destruction in 70 AD. And it seems to reason that He was teaching this in the Temple area to emphasize that point. Also, many people forget that Jesus had taught part of this to the disciples in Luke 17: 22-37, which would assist fill in the gaps in the Discourse He taught later. It always seemed unusual to me that if Jesus instructed people to run when they saw the troops around Jerusalem, how could they witness the Abomination of Desolation in the Temple if they were the same event? It appears that He was referring to two distinct occurrences, and we know that the Antichrist was not revealed at the time.