From The Gospel of Mark by Mary Healy, reflecting on Mark 13: 14
The desolating abomination is an expression from Daniel (9:27; 11:31; 12:11), where it alludes to the terrible sacrilege committed by the Syrian ruler Antiochus IV Epiphanes in 167 BC. After plundering Jerusalem, this infamous tyrant erected an idol of the Greek god Zeus on the altar of sacrifice in the temple (see 1 Macc 1:31, 54–59). A desolating abomination is one so egregious that it leads to the utter destruction of the temple and city, turning it into a desolate wasteland. Here that tragic event of the past is viewed as a foreshadowing of the final desecration of the temple that will lead to its destruction by the pagan armies of Rome (see Matt 24:15; Luke 21:20). Standing where he should not is precisely in the temple sanctuary, the holy place where the living God is worshipped. The masculine “he” suggests that this evil will be carried out by an individual, perhaps a military general, who is a kind of anti-Messiah figure (see 2 Thess 2:3–4).
Let the reader understand is probably intended as part of Jesus’ discourse, calling his disciples to pay close attention to hidden clues in the book of Daniel (see Matt 24:15). According to Daniel, both the sacrilege and the ensuing destruction, although carried out by wicked men, are a consequence of the sins of God’s people (see Dan 9:24). But God allows these disasters so that his people can be “refined, purified, and tested” (Dan 12:10). Jesus is hinting that the appearance of a horrendous sacrilege will signal the onset of a most devastating period of tribulation by which God’s people will be severely tried.