To help us begin to understand today's and tomorrow's readings, I offer this bit of information from the Daily Bible Study Commentary Series by William Barclay:
"In this chapter there are various strands of thought. The gospel writers had a way of collecting Jesus' sayings on any subject. It was a wise way to write and excellent for teaching purposes. Here Mark, as it were, collects Jesus' sayings about the future. Now even a cursory reading, with no special knowledge, shows that, though all these sayings were about the future, they were not all about the same things. There are in fact in this chapter five different strands.
There are prophecies of the destruction of Jerusalem. We get them in verses 1 and 2, 14-20. Jesus foresaw the end of the holy city. As we shall see, Jesus was right. Jerusalem fell in A.D. 70. The Temple was destroyed and the most terrible things happened.
There is warning of persecution to come. We get that in verses 9-13. Jesus foresaw that his followers would have to go through the most heart-breaking and soul-searing experiences, and he warned them in advance.
There are warnings of the dangers of the last days. We get them in verses 3 to 6 and 21 and 22. Jesus saw quite clearly that men would come who would twist and adulterate the Christian faith. …He wished to defend his people in advance from the heresies and lies which would invade the Church.
There are warnings of the Second Coming. Now, these warnings of the Second Coming are dressed in the language which has to do with the day of the Lord. We get them in verses 7 and 8 and 24 to 27. The imagery of the day of the Lord and of the Second Coming are inextricably mixed up.
There are warnings of the necessity to be on the watch. We get them in verses 28-37. If men live in the shadow of eternity, if they live with the constant possibility of the intervention of God, if they live with the prospect of the consummation of the coming of Christ ever before them, if the times and the seasons are known only to God, there is the necessity ever to be ready."