Which events in Jesus' life and future were already foretold in the Old Testament?
The Old Testament prophets foretold His suffering, death, resurrection, ascension, and coming again. Specifically, Scripture predicted He would be delivered to the Gentiles, mocked, spitefully entreated, spit upon, scourged, put to death, and rise again the third day. Psalms and Isaiah contain these prophetic aspects, though the disciples understood none of it at the time.
Les explains from Luke 18 that Jesus took the Twelve aside and said they were going up to Jerusalem, where all things written by the prophets concerning the Son of Man would be accomplished. Les stresses that everything about to take place had already been foretold: His suffering, death, resurrection, ascension, and coming again. He notes that Psalms is full of these prophetic aspects, and Isaiah and the other prophets also spoke of them. The specific predictions included being delivered to the Gentiles, mocked, spitefully entreated, spit upon, scourged, put to death, and raised the third day. Yet the disciples understood none of it, even though they knew the Old Testament; as Les says, they should have known, but they did not, and were totally unsuspecting.
Then he took unto him the twelve, and said unto them, Behold, we go up to Jerusalem, and all things that are written by the prophets concerning the Son of man shall be accomplished.