NKJ Matthew 13:10-17 1And the disciples came and said to Him, "Why do You speak to them in parables?"
11 He answered and said to them, "Because it has been given to you to know the mysteries of the kingdom of heaven, but to them it has not been given.
12 "For whoever has, to him more will be given, and he will have abundance; but whoever does not have, even what he has will be taken away from him.
13 "Therefore I speak to them in parables, because seeing they do not see, and hearing they do not hear, nor do they understand.
14 "And in them the prophecy of Isaiah is fulfilled, which says:`Hearing you will hear and shall not understand, And seeing you will see and not perceive;
15 For the hearts of this people have grown dull. Their ears are hard of hearing, And their eyes they have closed, Lest they should see with their eyes and hear with their ears, Lest they should understand with their hearts and turn, So that I should heal them.'
16 "But blessed are your eyes for they see, and your ears for they hear;
17 "for assuredly, I say to you that many prophets and righteous men desired to see what you see, and did not see it, and to hear what you hear, and did not hear it.
Their hearts had grown dull.
Their ears are hearing with difficulty.
They have closed their eyes. Active voice verb. They are doing this. And this is pivotal.
If they'd open their eyes they could see > their ears could hear > their hearts could understand > they would turn > and Jesus would heal them.
They didn't need a new heart. They needed to open their eyes and see what was in front of them as others had. The time had come that many prophets and righteous men had desired to see & hear, but but did not see and hear it because it was not God's timing.
The ones who did not close their eyes and the many before them who desired to see and hear, stand as a witness against these with the dull hearts and closed eyes.
Jesus had given all in Israel many chances. The signs He did per John's Gospel that GJohn is written to inform of are said to be signs that Israel was to know could only be done by Messiah. At some point He in essence said 'enough' and He began to teach in parables so whatever the ones who were closing their eyes had, would be taken from them.
At this point I'd consider dull hearts becoming hardened.