Hardness of heart is a callousness toward God, His will and that which He loves. We exhibit a hardness of heart when our will supercedes God's will. It is a volitional act on our part. The depth of hardness is accumulative.
For example, God clearly says that He will harden Pharoah's heart when Moses goes to get God's people out of Egypt. Many people believe that God prevented Pharoah from responding to His will. They see a divine will be imposed upon a people who are not His. They see God choosing to damn a person. I don't see it that way.
A person's heart is hardened when he or she refuses God's presence, His Word or His will. God was clearly showing Pharoah that he must let His people go. Yet, God knew that no matter what He did, Pharoah would never let His people leave Egypt. The plagues were not attempts to get Pharoah to relent. They were testimonies for God's people to believe. On one hand, Pharoah was hardening his heart by refusing to respond to God's will. On the other, God's people's faith was growing. Moses had enough trouble in the wilderness with these people. How hard would it have been if they had not seen God work?
Pharoah's heart got harder each time he refused to listen to God. God is responsible for hardening Pharoah's heart because He sent the plagues so that everyone would clearly understand His will. All who refuse to respond to God's presence, will and those He loves will harden their hearts.
One Sabbath Jesus goes to the synagogue to find a man with a withered hand. The Pharisees waited to see if He would heal on that day. He asked them if it was right to do good on the Sabbath. They remained silent. They failed to respond beyond their law even though God loved this man with the withered hand. It says that Jesus grieved over the hardness of their hearts.
My heart is hard at times. I can't be selfish or proud and do God's will. I sometimes choose being selfish and proud. I eventually reject selfishness and pride. I wonder why I ever embraced them. A hard heart shuts God out. It gets very lonely without Him. I relent and repent and He takes me back. The hardness is broken again.
Your heart gets a little harder each time you refuse to respond to God. Eventually it can get so hard that you no longer notice that God is absent from your life. At least, that's how it feels.
How about it? Where is God right now? Is He close or have you just been pretending to have Him near? Have you refused to respond to something He is telling you?
He stands at the door and knocks. Will you let Him come in?