The entire theme of the book of Mark, in Chapter 8 of the New Testament, centers on Jesus' miracles. He does things that amaze many people: he takes a few loaves and small fish and feeds the multitudes. While many are amazed, still there are others who doubt. The Pharisees are threatened by Jesus and are always looking for ways to trip him up. They ask him to show them that he is the Christ.
The Pharisees came and began to question Jesus. To test him, they asked him for a sign from heaven. (v. 11)
Jesus is plainly frustrated:
Why does this generation ask for a miraculous sign? (v. 12)
Jesus refuses to give the Pharisees what they want. Jesus speaks to his disciples and looks to see if they have true understanding, and apparently his concern for a "generation" looking for signs and proof reaches to the disciples.
It appears that the disciples take everything literally, when Jesus speaks figuratively, sometimes with metaphors—parables. Throughout all the time they have spent together, the disciples still don't understand completely what Jesus has been trying to teach them, and his time is limited.
He struggles with what they still do not grasp. They discuss the fact that they have no bread, but Jesus reminds them of the miracle with the loaves and fish. Do they really believe that bread matters? If they needed bread, Jesus could easily provide it: weren't they paying attention? He asks...
Do you have eyes but fail to see, and ears but fail to hear? (v. 18)
Jesus is wondering what else needs to do. They travel on and he heals a blind man. About the blind man, the author notes...
...his eyes were opened, his sight was restored, and he saw everything clearly. (v. 25)
This is literally what happens, but symbolically, this could also refer to what Jesus is hoping will happen to the disciples. The disciples are unable to see what Jesus is trying to teach them: he hopes their eyes will be opened to see beyond the literal, that they will understand through his teachings—to "see everything clearly."
So as they move on, Jesus asks what others are saying about him—also hoping the men will understand, for certainly Christ knows what is being said. They report:
Some say John the Baptist; others say Elijah; and still others, one of the prophets. (v. 28)
It is not surprising that the uninformed would wonder and guess as to who Jesus is. It is something that Jesus probably expects the disciples, who spend so much time with him, should know. He asks them:
“But what about you?” he asked. “Who do you say I am?” (v. 29)
Peter identifies Jesus as "the Christ." And Jesus tells the disciples not to tell anyone.
Some scholars note that Jesus is, in fact, also concerned about the disciples' lack of understanding with regard to Jesus' miracles:
This may indicate that before Jesus dies, he wants to make sure that his disciples truly understand the meaning of his teachings, their responsibilities after he is gone and the intent of his death on the cross.