One conversation in the comments on a post a few back reminded me of a question of a similar nature that piqued my own curiosity a little while ago.

What did Jesus mean when He said:

So when you see standing in the holy place 'the abomination that causes desolation,' spoken of through the prophet Daniel—let the reader understand— then let those who are in Judea flee to the mountains.

(Boldness mine)

This oddity is recorded in Matthew 24:15-16 and Mark 13:14

My question is, "What reader?" Isn't Jesus speaking privately to Peter, James, John, and Andrew? Mark 13:3-5

Is this like a little parenthetical aside by the author? If Jesus actually spoke those words, was He referring to the reader of the Book of Daniel? Was He referring to me myself, the reader of the Gospels of Matthew and Mark?

And what is meant by 'understand'? I would think it's assumed that if you're saying (or writing) something to somebody then you want them to understand. Why say it?