Continued from yesterday and the day before...
To a large extent, many
of these questions are unanswerable. We are plodding through them to get
a sense of exactly what we are dealing with here, what the possibilities are
and which are more and less likely. As we continue this troublesome
journey, we notice interestingly that Luke 21 has seriously toned down the
immanent expectation of Mark 13. For well over a century, most gospel experts have concluded that Luke likely used Mark as a major source when writing. We can thus see Luke's mind at work in where he seems to edit Mark's text.
For example, if Mark and Matthew seem to blur the events surrounding the destruction of the temple with Christ's second coming, Luke has apparently edited Mark to focus almost exclusively on the destruction of Jerusalem in AD70. So Mark 13:14 is somewhat ambiguous: "When you see the abomination of desolation standing where it should not be" (NASB). After Luke's editing, it reads like this: "When you see Jerusalem surrounded by armies, then recognize that her desolation is near" (Luke 21:20).  Luke has made it clearer that this event took place when the Romans destroyed Jerusalem in AD70.
Similarly, Luke has apparently removed statements in Mark like 13:19: "in those days there will be suffering, such as has not been from the beginning of the creation that God created until now, no, and never will be" (NRSV; this verse should have followed Luke 21:23). Luke also removes Mark 13:20: "if the Lord had not cut short those days, no one would be saved" (should also have appeared before Luke 21:24). The effect is to limit the scope of catastrophe in Mark and Matthew. Now we hear of the "times of the Gentiles" (Luke 21:24), a period during which the Gentiles will trample on Jerusalem in between the the time when the first part of the prophecy is fulfilled and when the kingdom will be restored to Israel at Christ's return (Acts 1:6). 
The impression we get is that we are not the first to wrestle with this question of when the kingdom of God will be here in full, when Christ will return to the earth to rule. Already in Luke we see early Christians wrestling with what some call the "delay of the parousia," the fact that Jesus did not return to earth as soon as his first followers initially anticipated. How did Jesus originally put it? To what extent did Mark interpret it? It seems impossible to answer these questions with any certainty from a historical perspective.
What we do have are the conclusions Christians have reached on these issues over the centuries. Does not the Holy Spirit come on the church at Pentecost? Perhaps it is not what Mark himself had in mind, but does not the birth of the church through the Spirit constitute "that the kingdom of God has come in power" (9:1)? Did not that generation see the destruction of Jerusalem and did not at least most of Mark 13 come true in their lifetimes? What if the events of the second coming were "telescoped" into material about the destruction of the temple?
It is often said that when you look at things through a telescope, things that are far removed from each other may look right next to each other. So it is often said of prophecy. We also know from Jonah also that God reserves the right to "change his mind" on prophecy. Predictions of destruction can be reversed because of human response--presumably, predictions of blessing can also.
We as Christians believe that Jesus inaugurated the rule of God on earth as it is in heaven. The kingdom was starting on earth in his ministry. We believe it came to earth spiritually with the pouring out of God's Spirit on the earth, beginning the age of the church, which has continued up until the present. And we believe that the kingdom will become entirely literal when Christ returns to earth and sets up an eternal kingdom here.
This is a theological perspective on the kingdom. It is the result of centuries-long Christian reflection on Jesus' words and the events that followed. The earliest followers of Jesus probably did not have a full understanding of how God was playing it all out. This is one of the blessings of having so many interpreters go before us. We have inherited the answers God has bequeathed to the church through them... often when we did not even realize there was a question.
 The clarity of Luke's paraphrase here is one reason to conclude that Luke-Acts was written after the destruction of Jerusalem in AD70. The desolation of Jerusalem by armies is a massive interpretation of the ambiguous, "abomination that causes desolation standing where it should not be."
 The freedom with which Luke paraphrases Mark should not worry us. All the evidence we have indicates that the New Testament authors felt free to paraphrase Scripture freely and interpretively, much as Eugene Peterson's paraphrase, The Message. We should not be bothered that Luke is doing it to statements of Jesus, in effect altering historical statements. Our sense of what is appropriate in history writing is simply not the same as theirs was. Luke is giving an inspired interpretation of Jesus.