Mark 9.30-32:
They went on from there and passed through Galilee. And he did not want anyone to know, (31) for he was teaching his disciples, and saying to them, “The Son of Man is going to be delivered into the hands of men, and they will kill him. And when he is killed, after three days he will rise.” (32) But they did not understand the saying, and were afraid to ask him. (ESV)
At this point in the gospel accounts of Jesus’ ministry, the disciples had seen absolutely amazing things. By this time, Jesus had appointed all twelve of his disciples, whom he also named apostles. As Jesus moved from place to place in Galilee and the Decapolis, people would come to Jesus and follow along with him. The disciples had seen a wide variety of miracles performed by Jesus. In addition to raising the dead and making the blind to see, Jesus had walked on the water and commanded the raging waves of the sea to become calm and they did so. All of these things demonstrated Jesus’ Lordship over all things of this physical earth. The disciples saw these things and were astounded. They did have faith in Jesus.
Yet when it came to Jesus’ mission and purpose of dying on the cross for the payment of the sin of the world, they did not understand. It is logical that they couldn’t quite grasp the idea that Jesus would suffer. They appear to have embraced the idea that the Messiah as king would conquer and win the victory over the Romans rather than suffer and die. In some respects it seems as though they willfully didn’t understand, because they would have to overlook the Suffering Servant passages in Isaiah. Isaiah chapter 53 being the most notable. They had other plans for Jesus. And so here it is once again. The truth that the victory of Jesus over sin and death and hell and the devil will be won by the death of Jesus on the cross, and his resurrection after three days.
All of this is hard to understand. They didn’t understand these things until after all of the events had happened, and we can only understand it by spiritual discernment given from heaven.