Thematic Symmetry of Matthew 24:15-21 with commentary - Interactive

15 “Therefore when you see the ABOMINATION OF DESOLATION which was spoken of through Daniel the prophet, standing in the holy place (let the reader understand),
16 then those who are in Judea must flee to the mountains.
17 Whoever is on the housetop
must not go down to get the things out that are in his house.
18 Whoever is in the field
must not turn back to get his cloak.
19 But woe to those who are pregnant and to those who are nursing babies in those days!
20 But pray that your flight will not be in the winter, or on a Sabbath.
21 For then there will be a great tribulation, such as has not occurred since the beginning of the world until now, nor ever will.

Commentary
Singularly great tribulation will begin when the abomination of desolation (spoken of by Daniel) is witnessed.
Those who witness this sign and are in Judea must flee, and the direction to pray about the timing suggests that prayer in advance will be beneficial for some.
This is where the structure of the passage pivots (chiasm, or, introversion) giving it emphasis and making it the center of attention. When you compare these matching elements at the pivot, it is immediately apparent that verses 17 and 18 resolve further into a repeating set. (ab a?b?. When we give consideration to how the matched elements compare and contrast, we are led to see verse 19 as a partial match, drawing us to inquire of the Author about the meaning of the asymmetrical pattern. Why are the women who are pregnant or nursing babies given no specific direction, like those others who might be on the housetop or in the field, which would be beyond the more general direction that is to pray about the timing of the flight, and in connection with that, of the ABOMINATION OF DESOLATION itself?