I am currently working through a series on the book of Mark and came across this gem of a quote on unbelief. Jesus travelled back to his hometown, Nazareth, with his disciples, and he carried out his typical practice of speaking in the synagogues. The people were surprised at his teaching, but then ultimately acted in disbelief of him. Mark 6:4-6 then presents what happened as a result.

Mark 6:4–6 (ESV)4 And Jesus said to them, “A prophet is not without honor, except in his hometown and among his relatives and in his own household.” 5 And he could do no mighty work there, except that he laid his hands on a few sick people and healed them. 6 And he marveled because of their unbelief. And he went about among the villages teaching.

What a shame! A Gentile demoniac in the preceding chapters, someone you would think would never believe in Jesus, did believe. Now here, those who were close to Jesus did not believe. James Edwards sums this up in his commentary on Mark in the Pillar New Testament Commentary Series.

“Amazed at their lack of faith.” What amazes God about humanity is not its sinfulness and propensity for evil but its hardness of heart and unwillingness to believe in him. That is the greatest problem in the world, and herein lies the divine judgment on humanity. Humanity wants a spectacular sign of God, or, like the devil, a great display of divine power (Matt 4:1–11; Luke 4:1–13). But it does not want God to become a human being like one of us (John 1:11). The people of Nazareth see only a carpenter, only a son of Mary, only another one of the village children who has grown up and returned for a visit. If only God were less ordinary and more unique, then they would believe. The servant image of the Son is too prosaic to garner credulity. God has identified too closely with the world for the world to behold him, too closely with the town of Nazareth for it to recognize in Jesus the Son of God. Humanity wants something other than what God gives. The greatest obstacle to faith is not the failure of God to act but the unwillingness of the human heart to accept the God who condescends to us in only a carpenter, the son of Mary.
James R. Edwards, The Gospel According to Mark, The Pillar New Testament commentary (Grand Rapids, Mich; Leicester, England: Eerdmans; Apollos, 2002), 174-75.