Matt 24:15

15 When, therefore, you see the abomination of desolation, which was spoken of through Daniel the prophet, standing in the holy place (let the reader understand)

when you see – the Greek word that has been translated as “see” really means “when you understand” – this is the meaning of the phrase “let the reader understand.”  We have no record of history that tells us that anyone understood the appearance of the Antichrist in his day. It is only today that we can “see.” This helps us understand Paul’s message in 2 Thess 2:3, “[The Day of the Lord] will not come unless . . . the man of lawlessness is revealed.” After the saints understand these things, then Christ will return.