Truly I tell you: Jesus is emphasizing the importance of his words.
this mountain: This probably refers to the Temple Mount, not the Mount of Olives. The judgment of the temple is the main focus in 11:12–25. Mark 12:9 will mention it again, and 13:1–37 describes it in detail. The reference to destroying the temple would later be raised at the trial (14:58) and crucifixion (15:29) of Jesus.