And as some spoke of the temple, how it was adorned with noble stones and offerings, he said, “As for these things which you see, the days will come when there shall not be left here one stone upon another that will not be thrown down.” And they asked him, “Teacher, when will this be, and what will be the sign when this is about to take place?” And he said, “Take heed that you are not led astray; for many will come in my name, saying, ‘I am he!’ and, ‘The time is at hand!’ Do not go after them. And when you hear of wars and tumults, do not be terrified; for this must first take place, but the end will not be at once.”
Then he said to them, “Nation will rise against nation, and kingdom against kingdom; there will be great earthquakes, and in various places famines and pestilences; and there will be terrors and great signs from heaven.
21:8. On hearing that Jerusalem is going to be destroyed, the disciples ask what sign will be given as a warning of these events (vv. 5–7). Jesus answers by telling them “not to be led astray,” that is to say, not to expect any warning; not to be misled by false prophets; to stay faithful to him. These false prophets will come along claiming to be the Messiah (“I am he!”). Our Lord’s reply in fact refers to two events which in the Jewish mind were interrelated—the destruction of the Holy City and the end of the world. This is why he goes on to speak of both events and implies that there will be a long gap between the two; the destruction of the temple and of Jerusalem are a kind of sign or symbol of the catastrophes which will mark the end of the world.
21:9–11. Our Lord does not want his disciples to confuse just any catastrophe—famine, earthquake, war—or even persecution with the signals of the end of the world. He exhorts them quite clearly: “Do not be terrified,” because although all this has to happen, “the end will not be at once;” in spite of difficulties of all kinds the Gospel will spread to the ends of the earth. Difficulties should not paralyze the preaching of the faith.
Friends, in today’s Gospel Jesus responds to questions about the end of the world. When will it come? What will happen? Why were the first Christians interested in these questions? The simplest and deepest answer is that they had experienced the end of the world—precisely in the dying and rising of Jesus.
Jesus came preaching the Kingdom of God, and the nations conspired against him. The old world seemed to conquer this new world that Jesus embodied. But then, in the resurrection, they saw that the old world—the world predicated upon death and the world that had done Jesus in—was now defeated.
So awed were they by the resurrection—and you can sense it in every book and letter of the New Testament—that they awaited the imminent arrival of the new state of affairs, the return of Jesus and the establishment of God’s kingdom. Though Jesus did not immediately return, the old world was over, broken, compromised, its destruction now just a matter of time.
– Bishop Robert Barron
May the virtues of faith, hope, and love go with you today – DV.
 Saint Luke’s Gospel, The Navarre Bible (Dublin; New York: Four Courts Press; Scepter Publishers, 2005), 169–170.