“For this people’s heart is waxed gross, and their ears are dull of hearing, and their eyes they have closed; lest at any time they should see with their eyes, and hear with their ears, and should understand with their heart, and should be converted, and I should heal them,” Jesus says in Matt 13:15 (KJV).
“And I will give them one heart, and I will put a new spirit within you; and I will take the stony heart out of their flesh, and will give them an heart of flesh: that they may walk in My statutes, and keep mine ordinances, and do them: and they shall be My people, and I will be their God. But as for them whose heart walketh after the heart of their detestable things and their abominations, I will recompense their way upon their own heads, saith the Lord God.” Ezekiel 11:19-21 (KJV).
I also came across this excellent post: