Another obstacle for contemporary readers might be the strangeness of apocalyptic passages. The purpose of apocalyptic passages, as a preacher friend of mine once said, can be summed up in the words of the pop song, "Hang on Sloopy, Sloopy, Hang on," recorded by The McCoys in 1965. It is a genre intended for persecuted groups that assures them, in vivid code language, of their imminent vindication through dramatic divine intervention. (See 21:12-17.)

The obstacle to Jesus' Advent in the days of the early Church was that people got so caught up in interpreting historical and natural events as signs of the end that they neglected the present time. They wouldn't have recognized Jesus if he had been standing right next to them, which, in fact and in Spirit, he was. The obstacle to preparing for Jesus' Advent today could be the same for some who pore over Nostradamus and the Left Behind series.

But for churches in countries where indifference to religion is more prevalent than persecution, maybe the loss of a sense of urgency is the obstacle to preparing for Advent. The Son of Man is coming, you say? I thought it was just the countdown of shopping days till Christmas.  I thought it was the consumer spending index and a plump, white bearded man in a red suit.

In Chapters 19 through 21, Jesus covers the whole emotional spectrum in seeking to motivate Jerusalem to prepare for the coming of the Son of Man. He weeps over Jerusalem (19:41-44); he seeks to cleanse it (cleansing of the Temple 21:19:45-48); and, finally, he foretells its destruction (21:20-24).

The Son of Man, many scholars feel, is the only Messianic label Jesus ever attached to himself. That sounds like something he would do, because this appellation had enough mystery in it that he could shape it to his own contours. Its existing meaning was "representative human," most explicitly mentioned in Hebrew Scriptures in Daniel (7:13f) and later connected with a future Messianic eschatological judge in such works as the Similitudes of Enoch and 4 Ezra.

Reliance on wealth and power. Following false teachings. Pointing our resources, time, and passion in a false direction with a false sense of urgency. Lacking any sense of urgency at all. All these obstacles to receiving Jesus now and preparing for his Advent in the future are implied in Luke 21:5-19.

The eloquent prediction of the coming of the Son of Man that comes shortly afterward, in Luke 21:25-28, underscores the challenge of our text for this morning.

Here a note from Joel Green's The Theology of the Gospel of Luke is illuminating:

Luke's emphasis on salvation in the present doesn't mean that he discounted the earlier Christian hope of the impending Parousia. In fact, Luke's presentation of the timing of the return of the Son of Man is more variegated. The end is very near, at hand, according to some texts (18:7-8; 21:31-32). According to others, a delay seems to be envisioned (12:45; 19:11). Two points are implied here. First, Luke has not simply collapsed the eschatological  hope of salvation into the present; the kingdom of God has a future element as well as a present one. Second, Luke's presentation of the Parousia defies oversimplification; as regards its timing, "it is not for you to know" (Acts 1:7). (Joel B. Green, The Theology of the Gospel of Luke, 97-98)

We can't be sure when, but we can be sure that the Son of Man is coming. That means that now is the time for us to stand up and raise our heads from our preoccupations with our wealth or lack thereof, our problems, our possessions, and our desire for personal influence and power. It is time to stop looking down. The best way to prepare for Advent is to identify these preoccupations as obstacles and then to stand up and raise our heads, because our redemption is drawing nigh.