Luke's third prediction of Jerusalem's fall is by far the most detailed (the others come in 13:34-35; 19:41-44). Because of the speech's importance and complexity, I take a slightly more didactic approach in my overview of it.
The speech's character emerges when one examines the parallels within the Synoptics. Parallels of this Olivet discourse occur in Matthew 24:1-35 and Mark 13:1-37. A comparison of these parallels shows how Luke has drawn out some additional teaching and made some distinct points. Some of these points emerge from the additional material Luke includes (vv. 18, 21-22, 24, 28 are certainly additional material; vv. 19-20, 23b-26, 34-36 are probably additional). Other emphases surface because of the way Luke has presented the traditional material. Where Matthew speaks specifically of the "abomination that causes desolation" (Mt 24:15), for example, Luke simply refers to the "desolation" (Lk 21:20).
The significance of these differences becomes clear as one carefully compares the accounts. Luke emphasizes the destruction of Jerusalem in A.D. 70 in a way the other Gospels do not. All the Synoptics anticipate the fall of Jerusalem in the way they introduce the discourse, but Luke focuses on the short-term event in a way Matthew and Mark do not. His temporal indicators (vv. 9, 12) draw the reader back toward the present before really focusing on the end in verses 25-28. A transition begins to appear in verses 20-24, but until verse 19 the focus is still on events before the judgment of the capital in A.D. 70, which is not yet the end.
How can Luke make such a shift? What Luke does is easier to understand when we grasp how divine history was read by the Jews, as well as by the prophets. The belief was that God's judgment followed certain patterns. How he judged in one era resembled how he would judge in another. Because God's character was unchanging and because he controlled history, such patterns could be noted. Thus deliverance in any era was compared to the exodus. One event mirrored another. Exilic judgments, whether Assyrian or Babylonian, were described in similar terms. This "mirror" or "pattern" interpretation of history has been called a typological-prophetic reading of the text, with the "type" reflecting a basic pattern in God's activity. This way of reading history sees events as linked and mirroring one another. Sometimes the events are described in such a way that we modern readers would not readily notice that distinct events are being discussed. Sometimes a text offers clarifying reflection after more events detailing God's program have been revealed.
Jesus' eschatological discourse links together two such events, the destruction of Jerusalem in A.D. 70 and the events of the end signaling his return to earth. Because the events are patterned after one another and mirror one another, some of Jesus' language applies to both. Mark and Matthew highlight the mirror's long-term image, while Luke emphasizes the short-term event. Either focus is a correct portrayal of Jesus' teaching. Failure to appreciate the typological background to this speech, however, has led to an overemphasis of one image against the other within the Synoptics. Some readers insist that the portrait of one writer must exactly match that of another. Instead, complementary emphases are possible. Appreciation of typology allows each author to speak for himself and allows the accounts of all the Synoptic writers to be viewed not in contradictory or one-sided terms but as complementary.
The speech makes several points. First, Luke clearly shows how the destruction of A.D. 70 is distinct from but related to the end. The two events should not be confused, but Jerusalem's destruction, when it comes, will guarantee as well as picture the end, since one event mirrors the other. Both are a part of God's plan as events move toward the end.
Second, Jesus' prophetic character is highlighted by this section. God is speaking through Jesus about unfolding events in the plan. Such prophetic gifts were highly respected in the ancient world (Philo Life of Moses 2.9.50-51).
Third, the Jewish nation's fate was clearly tied to its reaction to Jesus. The reader is not to question that the events Jesus describes will result from the nation's failure to respond to him (19:41-44). In fact, if one were to ask why Jerusalem was being judged, Luke has given many reasons. It is filled with hypocrisy (11:37-54), has oppressed the poor (18:7; 20:47), has rejected Messiah (13:33-34; 20:13-18), has missed the day of visitation (19:44), has rejected the gospel (Acts 13:46-48; 18:5-6; 28:25-28) and has slain God's Son (Lk 9:22; 18:31-33; 19:47; 20:14-19; 22:1-2, 52; 23:1-25; Stein 1992:521).
Fourth, the passage offers reassurance to disciples that God will enable them to face persecution and deliver them from it, whether by giving them words to say in their own defense or by saving them after martyrdom.
Fifth, the call is to remain steadfast because God is in control.
So the speech offers information and exhortations. It provides a general outline but not a detailed, dated calendar of future events. Such a general portrait without detailed dates is a common form for biblical apocalyptic material. We must be careful not to get more specific than Scripture does about the events of the future. Even though the portrait Jesus gives is general, he is saying, in effect, "Rest assured, God's plan is being fulfilled."
For simplicity's sake I have split the speech into two parts, though it is really one discourse: the events associated primarily with Jerusalem's fall (vv. 5-24) and the return and its significance (vv. 25-38).