The Bible has many warnings not to harden your hearts because it is possible to harden your hearts through sin, unbelief, and disobedience..
The LORD says, “Don’t harden your hearts as Israel did at Meribah,
as they did at Massah in the wilderness.
For there your ancestors tested and tried my patience,
even though they saw everything I did.
For forty years I was angry with them, and I said,
‘They are a people whose hearts turn away from me.
They refuse to do what I tell them.’
So in my anger I took an oath:
‘They will never enter my place of rest.’” (Psalm 65:8-11 NLT)
Do not harden your hearts through the deception that lead to destruction. This is the opposite of the gospel of rest. Instead be careful. Trust God to lead you throughout your life.
You should therefore be most careful, my brothers, that there should not be in any of you that wickedness of heart which refuses to trust, and deserts the cause of the living God. Help each other to stand firm in the faith every day, while it is still called “today”, and beware that none of you becomes deaf and blind to God through the delusive glamour of sin. For we continue to share in all that Christ has for us so long as we steadily maintain until the end the trust with which we began. These words are still being said for our ears to hear: ‘Today, if you will hear his voice, do not harden your hearts as in the rebellion’. (Hebrews 3:12-18 PHILLIPS)
If things aren’t working out for you. If you feel like you are fighting against God or He is fighting against you. If you have hardened your heart in rebellion to God, stop right now and take a moment to get right with God.