Luke 24:25
Then Jesus said to them, "You foolish men! How slow your minds are to believe everything the prophets have spoken [in their writings]!
Mark 7:18
He said to them, "Are you also as lacking in understanding [as the others]? Do you not understand that whatever enters a person's body from the outside cannot [spiritually] corrupt him?
Mark 8:17-18
Jesus, being aware of what they were thinking, said, "Why are you reasoning about not having any bread? Have you not yet perceived or understood? Have your hearts become insensitive?
Mark 9:19
Jesus said to them, "You generation of faithless people How long must I be with you [i.e., before you understand]? How long do I have to be patient with you? Bring the sick boy to me."
Mark 16:14
Later on Jesus showed Himself to the eleven apostles as they sat [i.e., reclined. See Matt. 23:6], eating a meal. He scolded them for their lack of faith and stubbornness because they refused to believe those who had seen Him [alive] after His resurrection.
Hebrews 5:11-12
[Now] we have many things to say about Melchizedek, but because of your slowness to grasp things, they are hard to explain.