The gospel of Mark is truly a great book with a wonderful way of telling the story of Jesus. He goes straightforward to his readers, and as Pastor Blankman said, he does not waste any time to declare that Jesus is the Son of God (1:1) but also he does not hesitate to show the disciples weakness along with the rest of the characters presented in this Gospel.
What we see in the disciples is a progressive understanding of Jesus and his teachings. I am glad that they did not get it right away, because we are not any different than them, we are slow learners and sometimes “heart hardened” (6:52) to believe even in the midst of great demonstration of the power of God.
In the gospel of Mark we can see that Jesus pay so much attention to the condition of our hearts. He even quotes Isaiah when is confronting the Pharisees and scribes: “This people honors me with their lips, but their hearts are far from me” (7:6) and also he says: “For it is from within, from human heart, that evil intentions comes” (7:21) he actually in chapter 8 confronted his disciples by telling them: “Do you still not perceive or understand? Are your hearts hardened? The psalmist also says: “Fools say in their hearts, “there is not God’ they are corrupt, they do abominable deeds; there is no one who does well” (Psalms 14:1)
So what is the cure that this Gospel presents for our flawed hearts? I think that actually in the incident, in which Peter was trying to advice Jesus against dying in the cross, Jesus himself told Peter that his troubles comes “For you are setting your mind (heart) not on divine things but on human things” (8:33) so according to this by the grace of God we have to learn how to transform and align our hearts with the divine purposes and ways.
How can we do that? Jesus answered: “If any want to become my followers, let them deny themselves and take up their cross and follow me” (8:34)