1 Samuel 10

Alma, in speaking of his father's repentance taught that -

"...according to his faith there was a mighty change wrought in his heart."
(Book of Mormon | Alma 5:12)

Samuel, the Lamanite said of his people -

"...that as many of them as are brought to the knowledge of the truth, and to know of the wicked and abominable traditions of their fathers, and are led to believe the holy scriptures, yea, the prophecies of the holy prophets, which are written, which leadeth them to faith on the Lord, and unto repentance, which faith and repentance bringeth a change of heart unto them—" (Book of Mormon | Helaman 15:7)

The mighty change of heart takes place as one repents and demonstrates faith in Jesus Christ. We don't change our hearts, Alma taught of the Savior -

"...he changed their hearts..." (Book of Mormon | Alma 5:7)

We see this same principle with Samuel prophesied to Saul -

"...the Spirit of the LORD will come upon thee..." (Old Testament | 1 Samuel 10:6)

and -

"...when he had turned his back to go from Samuel, God gave him another heart..." (Old Testament | 1 Samuel 10:9)

More than anything, I believe the final judgement will greatly be hinged on the nature of our heart.