Matthew 24:15 When ye therefore shall see the abomination of desolation, spoken of by Daniel the prophet, stand in the holy place, (whoso readeth, let him understand: )
Mark 13:14 But when ye shall see the abomination of desolation, spoken of by Daniel the prophet, standing where it ought not, (let him that readeth understand,) then let them that be in Judaea flee to the mountains:
It seems to me we need to go to the book of Daniel in order to find out what Jesus was meaning here, rather than trying to determine that from Luke 21.
All of the following passages involve desolation.
Daniel 8:13 Then I heard one saint speaking, and another saint said unto that certain saint which spake, How long shall be the vision concerning the daily sacrifice, and the transgression of desolation, to give both the sanctuary and the host to be trodden under foot?
Daniel 9:26 And after threescore and two weeks shall Messiah be cut off, but not for himself: and the people of the prince that shall come shall destroy the city and the sanctuary; and the end thereof shall be with a flood, and unto the end of the war desolations are determined.
27 And he shall confirm the covenant with many for one week: and in the midst of the week he shall cause the sacrifice and the oblation to cease, and for the overspreading of abominations he shall make it desolate, even until the consummation, and that determined shall be poured upon the desolate.
Daniel 11:31 And arms shall stand on his part, and they shall pollute the sanctuary of strength, and shall take away the daily sacrifice, and they shall place the abomination that maketh desolate.
Daniel 12:11 And from the time that the daily sacrifice shall be taken away, and the abomination that maketh desolate set up, there shall be a thousand two hundred and ninety days.
All of the following passages involve abomination.
Daniel 9:27 And he shall confirm the covenant with many for one week: and in the midst of the week he shall cause the sacrifice and the oblation to cease, and for the overspreading of abominations he shall make it desolate, even until the consummation, and that determined shall be poured upon the desolate.
Daniel 11:31 And arms shall stand on his part, and they shall pollute the sanctuary of strength, and shall take away the daily sacrifice, and they shall place the abomination that maketh desolate.
Daniel 12:11 And from the time that the daily sacrifice shall be taken away, and the abomination that maketh desolate set up, there shall be a thousand two hundred and ninety days.
IMO then, what Jesus was referring to in the Discourse has to do with all of the above passages I provided from the book of Daniel.
According to Daniel 11:31 and Daniel 12:11, the abomination is something that is placed that maketh desolate and is something that is set up. That doesn't sound like an army surrounding a city to me.
I think we need to take ALL of Jerusalem's past into account in order to get an idea as to what applies to the NT era and what had been already fulfilled from Daniel's prophecy. Jesus is quoted as saying this (so this seems to be the clear single sign that He was instructing His generation of followers to look for to mark their flight out of Jerusalem):
In Matthew 23:38, Jesus summed up what had become of Jerusalem in His lament over that city. Although formerly God’s house, Jesus now spoke of Jerusalem (and/or the temple) as
Jeremiah 12:7-11 ~
“I have forsaken My house, I have left My heritage; I have given the dearly beloved of My soul into the hand of her enemies… ‘Many rulers have destroyed My vineyard, they have trodden My portion underfoot; They have made My pleasant portion a desolate wilderness. They have made it desolate; Desolate, it mourns to Me; The whole land is made desolate, because no one takes it to heart”
Timeline of Jerusalem (taken from That the World May Know)
Approx. 2,000 BC: Abraham was sent to the Moriah area to sacrifice Isaac. Jerusalem was later built on the mountain named Moriah.
Approx. 1,000 BC: David captured the Canaanite city of Jebus (2 Sam. 5:6-7) and named it the City of David, which he made his capital (1 Chron. 11:7). He selected the temple site on Mount Moriah, where he built an altar.
Approx. 950 BC: Solomon built the temple on the Mount Moriah site chosen by David. After the Ark of the Covenant, the resting place of God's presence, was moved into the temple, the people prayed for God's presence, and God sent fire to consume their sacrifice (2 Chron. 7:1-3).
586 BC: The Babylonians destroyed the temple and took many Israelites captive.
Approx. 500 BC: Cyrus, the king of Persia, decreed that the Israelites could return to Jerusalem. Under Ezra and Nehemiah's leadership, the temple was rebuilt. Since there was no Ark of the Covenant, the Holy of Holies was left empty. The Jews rejoiced when the Torah was read (Neh. 8:17).
322 BC: Jerusalem became part of Alexander the Great's empire. Antiochus, king of the Syrians, outlawed the Sabbath, circumcision, and study of the Torah. He defiled the altar by sacrificing pigs on it.
165 BC: The Maccabean revolt against the Greek army brought Jerusalem under Jewish control once again and the menorah was re-lit. Descendants of the Maccabees expanded the Temple Mount.
63 BC:The Romans took control of Judea.
37-4 BC:Herod the Great, the Roman king of Israel, lavishly expanded the Temple Mount.
Approx. AD 30: The Sadducees had Jesus crucified. The Holy Spirit came to the disciples in the temple courts, and the veil in front of the Holy of Holies tore from top to bottom, symbolizing that all believers now had access to God's presence through Jesus.
AD 44: Herod Agrippa, grandson of Herod the Great, died. Rebel Jews began to kill Romans and Jews who cooperated with Rome. Roman governors became increasingly cruel, and the temple priesthood became more corrupt as they looked to Romans for security and support.
AD 66: A Gentile offered a "pagan" sacrifice next to the synagogue in Caesarea. Jerusalem authorities decided to end all sacrifices and allowed Roman troops to raid the temple treasury.
When the Jews protested, Florus, the Rome-appointed governor, sent troops who killed innocent civilians. This sparked a Jewish revolt that pushed the Roman troops out of Jerusalem. When the Romans in Caesarea heard what happened, they slaughtered 20,000 Jews in a day's time.
AD 68: Ultra-nationalistic Jews (Zealots) appointed their own temple priest and slaughtered the Sadducee priests who resisted.
AD 70: Roman troops destroyed Jerusalem and burned the temple. Over a million Jews were executed, sold into slavery, or captured for games in the arena.
AD 131: A second Jewish revolt began.
AD 135: Rome squashed the second revolt and outlawed the Jewish religion. The Jews became a people without a country.
~ Temple Events
The Jewish Revolts: THE REVOLT BEGINS While Christians and Jews were thrown to the wild animals by the emperor Nero in Rome, violence flared in Judea. In Caesarea, a conflict between Jews and Gentiles over activities next to the synagogue had been brewing for some time. In AD 66, on the Sabbath day, a Gentile offered a pagan sacrifice next to the entrance to the synagogue. There was an outcry from the citizens of Caesarea. The authorities in Jerusalem decided to end all foreign sacrifices, including the one for Caesar himself, in the Temple. Florus the governor, who lived in Caesarea, came to Jerusalem with troops, entered the Temple treasury, and took a large amount of gold. When people gathered to protest, Florus unleashed his legionnaires on innocent civilians of the city. The Jewish Revolts