Hebrews 5:11
About this we have much to say which is hard to explain, since you have become dull of hearing.
2 Peter 3:16
He writes the same way in all his letters, speaking in them of these matters. His letters contain some things that are hard to understand, which ignorant and unstable people distort, as they do the other Scriptures, to their own destruction.
Matthew 13:15
For this people's heart has grown dull. And their ears are hard of hearing, and their eyes they have closed, lest they should see with their eyes, and hear with their ears, and they understand with their hearts, and turn so that I should heal them.'
Mark 8:17-18
Being aware of it, Jesus said to them, "Why do you discuss the fact that you have no bread? Do you not yet perceive or understand? Are your hearts hardened?
Mark 8:21
He said to them, "Do you not yet understand?"
Luke 24:25
And he said to them, "O foolish men, and slow of heart to believe all that the prophets have spoken!
John 6:6
But this he said to test him, for he himself knew what he would do.
John 16:12
"I have many more things to say to you, but you cannot bear them now.
Acts 28:27
For this people's heart has become dull, and with their ears they scarcely hear, and their eyes they have closed; otherwise they might see with their eyes, and hear with their ears, and understand with their heart and turn, and I would heal them."'