Did the apostles understand Jesus when he spoke about his death and resurrection?
No. The apostles did not understand Jesus' predictions of His death and resurrection. Scripture says that saying was hidden from them, and they understood none of those things. They were not expecting the crucifixion, did not know He would rise, because God sovereignly kept them ignorant of it at that time.
Les explains that Jesus' words about His death and resurrection went off the apostles like water off a duck's back; it never registered. Quoting Luke, he notes they understood none of these things, and the saying was hid from them. So when the crucifixion came, they were not expecting it. When He died and was placed in the tomb, they did not camp out until resurrection morning, because they did not know He was going to rise from the dead. Les adds that maybe they should have, but they didn't, because God had sovereignly kept them ignorant of it. He also stresses that God opens understanding; it is not man's doing.