Mat 24:16 Then let them who are in Judea flee into the mountain:
Mat 24:17 Let him who is on the housetop not come down to take anything out of his house:
Mat 24:18 Neither let him who is in the field turn back to take his clothes.
Mat 24:19 And woe unto those who are with child, and those who are nursing in those days!
Mat 24:20 But pray you that your flight be not in the winter, neither on the sabbath day:

This key to this section is the desire to flee or escape, leaving behind your own life. The ideas here can be applied to the fall of Jerusalem or any civilization since, but it can also be applied the death of a single person.

The first idea in verse 16 is leaving your known life behind. Judea is the known country of civilization. The mountains are the unknown, wilder, harder territory. The original Greek doesn't have any of the "connective" tissue that turns these lines into advice. A direct translation is, "Then in Judea escape to the mountains." This is a statement of necessity not a suggestion. You don't go to the mountains because you like the mountains, you go because you must. You have nowhere else to escape to.

The next few verses emphasize both the suddenness of this change and how it turns all your priorities upside down. Everything is left behind. Your house, which is the symbol for family, your fields, which is Christ's symbol for material wealth, even your clothes, which Christ uses as a symbol for your status in society, are all left behind.

However, the sadest part of this escape is its affect on those who are dependent on us. Viewing this section as about the fall of civilization is sad, but viewing it as about the end of life makes it tragic. The greatest sadness is when pregnant women and new mothers die.

The last verse is simply about our hope (and his hope for each of us) for an easy escape, an easy transition, and an easy death. The winter is about the indifference of nature to our stuggles. The Sabbath is about the indifference of society to our struggles. (Christ in all his teaching makes it clear that he considered the various restrictions that religious leaders put on the Sabbath as artificial, more about their own self-importance and self-righteousness than about God. Christ's view was the God created the Sabbath for man, not the other way around.)

This last line also makes the point that Christ isn't talking about just one event. He is talking about a type of life-changing collapse that happens at various times to various civilizations and to every individual in their own time. However, even when we apply these ideas to the final end of the world, the nature of things assures that it will happen at different times in different places. When it is winter in the north, it is summer in the south. When it is the Sunday in the West, it is Monday in the East. The point here is that by the very nature of the design of the world, an event happens at different times in different livers, even when it happens at the same, exact moment.

"Flee" is from pheugô, which means "to flee," "to take flight," "to escape," and "to flee one's country."
"Housetop" is from dôma, which means "house" or "household."
"Come down" is from katabainô, which means "dismount," "come down," "go down," and "step down." It is a metaphor for "attain" and with the word "end" (telos) means "attaining one's end."
"Winter" is from cheimôn, which means "winter," "stormy weather" and "storm."