'Dull' in the Bible

For this nation’s heart has grown hard,And with their ears they hardly hear,And they have [tightly] closed their eyes,Otherwise they would see with their eyes,And hear with their ears,And understand with their heart, and turn [to Me]And I would heal them [spiritually].’

And He said, “Are you still so dull [and unable to put things together]?

because they had not understood [the miracle of] the loaves [how it revealed the power and deity of Jesus]; but [in fact] their heart was hardened [being oblivious and indifferent to His amazing works].

And He said to them, “Are you, too, so foolish and lacking in understanding? Do you not understand that whatever goes into the man from outside cannot defile and dishonor him,

Then Jesus said to them, “O foolish men, and slow of heart to trust and believe in everything that the prophets have spoken!

“He has blinded their eyes and He hardened their heart, to keep them from seeing with their eyes and understanding with their heart and being converted; otherwise, I [their God] would heal them.”

“For the heart (the understanding, the soul) of this people has become dull (calloused),And with their ears they scarcely hear,And they have shut their eyes [to the truth];Otherwise they might see with their eyes,And hear with their ears,And understand with their heart and return [to Me],And I would heal them.”’

Let no one deceive himself. If anyone among you thinks that he is wise in this age, let him become a fool [discarding his worldly pretensions and acknowledging his lack of wisdom], so that he may become [truly] wise.

But [in fact] their minds were hardened [for they had lost the ability to understand]; for until this very day at the reading of the old covenant the same veil remains unlifted, because it is removed [only] in Christ.

Concerning this we have much to say, and it is hard to explain, since you have become dull and sluggish in [your spiritual] hearing and disinclined to listen.