Mark 7:18

7:18 He said to them, “Are you so foolish? Don’t you understand that whatever goes into a person from outside cannot defile him?

Mark 8:17-18

8:17 When he learned of this, Jesus said to them, “Why are you arguing about having no bread? Do you still not see or understand? Have your hearts been hardened? 8:18 Though you have eyes, don’t you see? And though you have ears, can’t you hear? Don’t you remember?

Mark 9:19

9:19 He answered them, “You unbelieving generation! How much longer must I be with you? How much longer must I endure you? Bring him to me.”

Mark 16:14

16:14 Then he appeared to the eleven themselves, while they were eating, and he rebuked them for their unbelief and hardness of heart, because they did not believe those who had seen him resurrected.

Hebrews 5:11-12

The Need to Move on to Maturity

5:11 On this topic we have much to say and it is difficult to explain, since you have become sluggish in hearing. 5:12 For though you should in fact be teachers by this time, you need someone to teach you the beginning elements of God’s utterances. You have gone back to needing milk, not solid food.