Verse 15 opens with "When therefore....", with an emphasis not in Mark (Mk 13,14)
The abomination of desolation in verse 15 refers to Daniel, Dn 9,27. "Let the reader understand" iindicates that the reader is to link it with current events.
This time of "when" is about taking precautions: verses 16-22. What is the advice in verse 16? See Genesis 19,15-17.
The message of the following verses is clear. For verse 18, see Gen 19,26.
The importance of the sabbath in verse 20 continues in Matthew's community.
Verse 21: see Daniel 12,1.
Who are the elect in verse 22?
Verses 23-24, see verses 5 & 11.
False prophets in verse 24 as in verse 11.
What is the message of verse 25-27?
For verse 27, see Exodus 19,16 or Ps 144,6.
Verse 28 is best left as obscure.
There is a noticeable change of language in verses 29-31. As usual, it is based on a range of Old Testament allusions:
verse 29: Is 13,10; Joel 2,10; 3,4; 4,15.
Verse 30: Daniel 7,13-14.
verse 31: Is 27,13; 1st Thessalonians 4,16.
The fig tree is one of the few trees in Palestine to shed its leaves in winter. See Song of Songs 2,11-13.
Verse 33 points to the evidence just described. For the approaching day of the Lord, consider Joel 1,15; 2,1 among other OT references.
"This generation" in verse 34 causes problems because we are now many generations on.
Verse 35 is a firm claim to authority for the words of Jesus. See 5,18 and Is 40,8 or Is 55,11.
Verse 36 underlines the point about the question of when. See 24,15 and look back at the disciples' question in 24,3.
Take alook at my response .
Now we can go on to read the next phase of the discourse, Mt 24,37-51.