Desire and capacity

There may be more, but I found two references in the Book of Mormon referencing the incredible change that took place as people became converted to Christ:

Mosiah 5, when King Benjamin completed his sermon (emphasis added)
1 And now, it came to pass that when king Benjamin had thus spoken to his people, he sent among them, desiring to know of his people if they believed the words which he had spoken unto them.

2 And they all cried with one voice, saying: Yea, we believe all the words which thou hast spoken unto us; and also, we know of their surety and truth, because of the Spirit of the Lord Omnipotent, which has wrought a mighty change in us, or in our hearts, that we have no more disposition to do evil, but to do good continually.

Alma 19, when Ammon's service and boldness had converted the people of Lamoni (emphasis added)
33 And it came to pass that when Ammon arose he also administered unto them, and also did all the servants of Lamoni; and they did all declare unto the people the selfsame thing—that their hearts had been changed; that they had no more desire to do evil.

Wouldn't that be nice?  To have no more disposition or desire to do evil?  I used to pray for that, that the Lord would take away any desire I had to ever sin again.  Not realistic in this life.

This life is designed to have us learn.  We learn by making mistakes.  Temptation will never be removed from us on Earth, because that's the primary way we make mistakes and learn from them.  I'm sure that Nephi also had no disposition to do evil, yet he was "easily beset" by temptations (2 Ne 4:18).  Paul certainly had a mighty change on the way to Damascus, and he still did the evil that he didn't want to do (Romans 7:19).  And though it's not specifically listed in the scriptures, I'm certain that every one of the people of King Benjamin and every citizen of Lamoni's kingdom sinned again at some point.
The Savior's sacrifice saves us from our sins, if that's what we desire.  The Atonement's power can overcome any and all of our sins, but not our agency, if what we desire is not Eternal Life.

The Mighty Change that we can experience in this life really can change our desires, but cannot, while on Earth, remove the sinful nature of the world we live in, nor of our need to learn to do good by sometimes doing evil.

We can want to do good continually, but we will always lack the capacity to do so. It gets frustrating, doesn't it?  To be able to want something and not have the ability to achieve it.  The Atonement gives us that ability, or rather, makes up for the fact that we lack it.

Repentance is the key.  In the end we'll be judged on our works and our desires.  And we'll probably have works that make it look like our desires weren't good.  By repenting daily for "the evil that I do" (Rom 7:19) I demonstrate that my desire is to do good, even if my actions don't always show it.

Alma 41 (emphasis added)3 And it is requisite with the justice of God that men should be judged according to their works; and if their works were good in this life, and the desires of their hearts were good, that they should also, at the last day, be restored unto that which is good.
4 And if their works are evil they shall be restored unto them for evil. Therefore, all things shall be restored to their proper order, every thing to its natural frame—mortality raised to immortality, corruption to incorruption—raised to endless happiness to inherit the kingdom of God, or to endless misery to inherit the kingdom of the devil, the one on one hand, the other on the other—
5 The one raised to happiness according to his desires of happiness, or good according to his desires of good; and the other to evil according to his desires of evil; for as he has desired to do evil all the day long even so shall he have his reward of evil when the night cometh.