'Heart' in the Bible

He who believes in the Son of God has the testimony in his own heart: he who does not believe God has made Him a liar, in that he has refused to accept the testimony which God has given about His Son.

Little children (believers, dear ones), guard yourselves from idols—[false teachings, moral compromises, and anything that would take God’s place in your heart].

My loved ones, while my thoughts were full of a letter which I was going to send you about our common salvation, it was necessary for me to send you one requesting you with all my heart to go on fighting strongly for the faith which has been given to the saints once and for ever.

Blessed (happy, prosperous, to be admired) is he who reads and those who hear the words of the prophecy, and who keep the things which are written in it [heeding them and taking them to heart]; for the time [of fulfillment] is near.

So keep in mind where you were at first, and be changed in heart and do the first works; or I will come to you, and will take away your light from its place, if your hearts are not changed.

See, then, that you have a change of heart; or I will come to you quickly, and will make war against them with the sword of my mouth.

And I gave her time for a change of heart, but she has no mind to give up her unclean ways.

So remember and take to heart the lessons you have received and heard. Keep and obey them, and repent [change your sinful way of thinking, and demonstrate your repentance with new behavior that proves a conscious decision to turn away from sin]. So then, if you do not wake up, I will come like a thief, and you will not know at what hour I will come to you.

To all those who are dear to me, I give sharp words and punishment: then with all your heart have sorrow for your evil ways.

How much she hath glorified herself, and lived deliciously, so much torment and sorrow give her: for she saith in her heart, I sit a queen, and am no widow, and shall see no sorrow.

“And behold, I am coming quickly. Blessed (happy, prosperous, to be admired) is the one who heeds and takes to heart and remembers the words of the prophecy [that is, the predictions, consolations, and warnings] contained in this book (scroll).”