'Hardened' in the Bible

“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.”

But when some were becoming hardened and disobedient [to the word of God], discrediting and speaking evil of the Way (Jesus, Christianity) before the congregation, Paul left them, taking the disciples with him, and went on holding daily discussions in the lecture hall of Tyrannus [instead of in the synagogue].

“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.”’

What then? Israel failed to obtain what it was seeking [that is, God’s favor by obedience to the Law], but the elect [those chosen few] obtained it, while the rest of them became hardened and callously indifferent;

But continually encourage one another every day, as long as it is called “Today” [and there is an opportunity], so that none of you will be hardened [into settled rebellion] by the deceitfulness of sin [its cleverness, delusive glamour, and sophistication].