'Heart' in the Bible

But because of your hardness and unrepentant heart you are storing up wrath for yourself in the day of wrath, when God’s righteous judgment is revealed.

On the contrary, a person is a Jew who is one inwardly, and circumcision is of the heart—by the Spirit, not the letter. That man’s praise is not from men but from God.

But thank God that, although you used to be slaves of sin, you obeyed from the heart that pattern of teaching you were transferred to,

that I have intense sorrow and continual anguish in my heart.

But the righteousness that comes from faith speaks like this: Do not say in your heart, “Who will go up to heaven?” that is, to bring Christ down

On the contrary, what does it say? The message is near you, in your mouth and in your heart. This is the message of faith that we proclaim:

If you confess with your mouth, “Jesus is Lord,” and believe in your heart that God raised Him from the dead, you will be saved.

One believes with the heart, resulting in righteousness, and one confesses with the mouth, resulting in salvation.