Hebrews 5:11
[Now] we have many things to say about Melchizedek, but because of your slowness to grasp things, they are hard to explain.
2 Peter 3:16
He spoke about these things in all of his letters, which contain some parts that are difficult to understand. [Because of this], ignorant and unstable people twist [his writings], just as they also do to the other Scriptures, to their own destruction.
Matthew 13:15
For these people's minds are dull, and their ears have difficulty hearing, and they have shut their eyes. For if this were not the case, they would perceive what they see with their eyes, and comprehend what they hear with their ears, and understand with their minds and would turn [back to God] again so I would heal them [from their sins].'
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 8:21
Then He said to them, "Do you not understand yet?"
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]!
John 6:6
Now He said this to test Philip, for He [already] knew what He was going to do.
John 16:12
"I still have many things to tell you, but you cannot bear [to hear] them at present.
Acts 28:27
For these people's minds are dull, and their ears are hard of hearing, and they have shut their eyes. For, if this were not the case, they would perceive what they see with their eyes, and understand what they hear with their ears, and comprehend with their minds, and would turn [back to God] again and I [God] would heal them [from their sins].'