Hebrews 5:11
Concerning Whom we have much to say and difficult to explain, since ye have become dull of hearing.
2 Peter 3:16
as also in all his letters, speaking in them of these things; in which are some things hard to be understood, which the ignorant and unstable wrest, as they do also the other Scriptures, to their own destruction.
Matthew 13:15
for the heart of this people was made gross, and with their ears they heard heavily, and their eyes they closed; lest they should see with their eyes, and hear with their ears, and understand with their heart, and turn, and I should heal them.'
Mark 8:17-18
And perceiving it, He saith to them, "Why are ye reasoning because ye have no bread? Do ye not yet perceive, nor understand? Have ye your heart hardened?
Mark 8:21
And He said to them, "Do ye not yet understand?"
Luke 24:25
And He said to them, "O inconsiderate and slow in heart to believe in all that the prophets spake!
John 6:6
And this He said, proving him; for He Himself knew what He was about to do.
John 16:12
"I have yet many things to say to you; but ye are not able to hear them now.
Acts 28:27
for the heart of this people was made gross; and with their ears they heard heavily; and their eyes they closed; lest at any time they should see with their eyes, and hear with their ears, and understand with their heart, and should turn, and I should heal them.'