'Heart' in the Bible

But because of your stubborn and unrepentant heart you are reserving wrath for yourself on the day of wrath, when God's righteous judgment will be revealed.

No, a person is a Jew inwardly, and circumcision is a matter of the heart, brought about by the Spirit, not by a written law. That person's praise will come from God, not from people.

I have deep sorrow and unceasing anguish in my heart,

Therefore, God has mercy on whomever he chooses, and he hardens the heart of whomever he chooses.

But the righteousness that comes from faith says, "Do not say in your heart, "Who will go up to heaven?' (that is, to bring the Messiah down),

But what does it say? "The message is near you. It is in your mouth and in your heart." This is the message about faith that we are proclaiming:

If you declare with your mouth that Jesus is Lord, and believe in your heart that God raised him from the dead, you will be saved.

For one believes with his heart and is justified, and declares with his mouth and is saved.