O fools.

Mark 7:18
"Are you still so dull?" He asked. "Do you not understand? Nothing that enters a man from the outside can defile him,

Mark 8:17, 18
Aware of their conversation, Jesus asked them, "Why are you debating about having no bread? Do you still not see or understand? Do you have such hard hearts? . . .

Mark 9:19
"O unbelieving generation!" Jesus replied. "How long must I remain with you? How long must I put up with you? Bring the boy to Me."

Mark 16:14
Later as they were eating, Jesus appeared to the eleven and rebuked them for their unbelief and hardness of heart, because they did not believe those who had seen Him after He had risen.

Hebrews 5:11, 12
We have much to say about this, but it is hard to explain, because you are dull of hearing. . . .