If our main source of Christian apocalyptic is the book of Revelation, we might not understand the message Mark is conveying in today's gospel pericope. We're liable to read something into it which isn't there.
Though Revelation also describes the "last days," it does so in the context of a theology which contradicts all other theologies in the Christian Scriptures. One day, while shopping, I saw a Mary Englebreit t-shirt sporting a biblical ecological message: "Do not damage the land or the sea or the trees." I was amazed when I saw it was from chapter 7 of Revelation - a book not noted for its ecological teachings. I quickly wandered into a nearby bookstore, picked up a Bible and checked it out. It actually was from Revelation 7, but it was only the first half of verse 3. Ms Englebreit had conveniently left out the rest. The next word in the verse is "until." The author basically says, "Don't do anything to the land, sea, or trees until I give the command, then wipe them out!" Now that's the book of Revelation I know - and don't love.
Of course, when one reads Daniel (the only apocalyptic book in the Hebrew Scriptures) one also finds lots of God-caused destruction. But as we hear in today's first reading, Yahweh doesn't get Yahweh's hands dirty in such a project. It's left to Michael to do the "cleaning up" before Yahweh's people receive their final reward.
Yet because we're in the Christian, not Hebrew Scriptures, it's appropriate for Dominic Crossan to point out how the revenge and destruction message of Revelation (and the Left Behind series based on it) is at odds with the message the gospel Jesus proclaims. As a Scripture scholar, and a Christian, Crossan can only speculate on the historical circumstances which enabled such a theology to be eventually accepted into the canon of the Christian Scriptures. I have no space here to present his speculations on how this book got into our Bible, but it's important to appreciate his concern.
Though chapter 13 contains Mark's apocalyptic "vision," his Jesus takes no revenge, nor destroys anything. His Jesus arrives on the scene only after humans and nature have wreaked havoc on the earth. He plays no role in either. Unlike Revelation, none of these calamities is looked upon as a punishment for evil people or a revengeful reward for the good folk. They're simply "stuff that the faithful in those days expected to happen before Jesus' second coming. Even many unbelievers thought the world's eventual end would be preceded by such natural catastrophes. Mark is simply saying, when that end comes, expect Jesus' arrival.
This rather peaceful picture of Jesus dovetails with the picture we find in our Hebrews reading. He's always "perfecting" his followers, even into eternity. As the author states, Jesus' "thing" is forgiveness, not vengeance. The text doesn't even say that Jesus physically made his enemies his footstool. They could have gotten themselves into that ignoble position by their own actions, without Jesus' help.
But there's still one troubling aspect in today's gospel. "Amen, I say to you," Jesus proclaims, "this generation will not pass away until all these things have taken place." Obviously "this generation" has passed, and we're still waiting for the Parousia. Until Luke writes - probably in the mid-80s - our Christian sacred authors seem to believe Jesus will triumphantly return in their lifetime. Second and third generation followers of the risen Jesus eventually had to change the way they looked at and lived their faith once they began to understand his Parousia would be indefinitely delayed.
Makes one wonder what "faith-changes" still await us in the future, changes not even our biblical writers could have anticipated.