What does Mark 8:18 mean?

After watching the disciples fuss over the fact that they have forgotten to bring bread, Jesus used the Socratic method to open their eyes to the fact that they are being obtuse. Here, He continues His questioning to accuse them of not paying attention.

"Eyes" is from the Greek root word ophthalmos. Although it means someone's literal eyes, it also represents a person's ability to know something. "See" is from the Greek root word blepo and is similar, as it means to see or to be able to understand, contemplate, and examine. "Ears"—ous—and "hear"—akouo—have similar literal and figurative definitions. "Remember" is from the Greek root word mnemoneuo and means "to call to mind."

The disciples have such a rigid idea of who Jesus is that they have not been able to reconcile his actions with their preconceived ideas of Him. In response, their brains have rejected the evidence in front of them. They seem to notice those things that appeal to them, like Jesus rebuking the religious leaders (Mark 2:18–28). They puzzle over events, like Jesus interacting with a Syrophoenician woman (Mark 7:24–30), that don't make sense. But they miss the nuances of His purpose as it is revealed in the very acts of power they witness and take part in (Mark 6:7–13). And Jesus' use of the words "do you…?" instead of "can you…?" indicates this behavior is at least partially intentional.

We are guilty of the same behavior. It is easier to take the bits of Scripture and of Jesus that agree with what we think of God. It's harder to incorporate His truths with our established worldview. The Old Testament associates such behavior with foolishness and senselessness (Jeremiah 5:21) and rebellion (Ezekiel 12:2). We, like the disciples, have a choice as to whether we trust God's truth or our interpretations.