What does the Bible say about hard hearts?

Scripture indicates that men's hearts are spiritually hardened due to sin and rebellion against God. In Jeremiah 17:9, it states, 'The heart is deceitful above all things, and desperately sick; who can understand it?' This highlights the necessity for divine intervention as human efforts are insufficient to change the heart towards God. Only the Lord can soften the heart and bring about genuine repentance and faith, as seen in Ezekiel 36:26 where God promises to give a new heart and spirit.