The gospel of Jesus Christ can change peoples desires and attitudes. Boyd K. Packer, President of the quorum of the 12 apostles said "a study of the Gospel will improve behavior quicker than a study of behavior will improve behavior"
As a missionary, being called to teach this "good news", we have the opportunity of seeing many people experience the joy of the gospel. This joy is a great motivator for them to make changes in their life to bring their lives in closer harmony with that of Jesus Christ. Thus fulfilling our purpose here in this life, which is to prepare to meet god. This change comes through sincere repentance. To repent is to change. When we repent, we say to our Father in Heaven that we are sorry for the things we have done and that we will be better from that point on.
I love the story in the Book of Mormon about a group of people who felt the joy of repentance, it is found in Mosiah chapters 2-5. I want to focus on a couple of scriptures, King Benjamin, a book of mormon prophet, has just taught about the Savior Jesus Christ and some of the things he would do, when he had finished speaking, the multitude felt the spirit and in Mosiah 4:2 they say "...O have mercy, and apply the atoning blood of Christ that we may receive forgiveness of our sins, and our hearts may be purified; for we believe in Jesus Christ, the Son of God, who created heaven and earth, and all things; who shall come down among the children of men." They have thus accomplished the first steps of repentance, acknowledging their sins, being sorry for their sins and asking for forgiveness. After this they felt the great blessing of the Atonement and the joy of repentance. "And it came to pass that after they had spoken these words the Spirit of the Lord came upon them, and they were filled with joy, having received a remission of their sins, and having peace of conscience, because of the exceeding faith which they had in Jesus Christ."
King Benjamin continued on and taught them more on repentance and forgiveness, and then comes my favorite part of this story. King Benjamin finishes his sermon and desires to know if they believed the words which he had spoken. They Replied, " 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." (Mosiah 5:2)
This is such a great blessing that the Lord has given us, that not only will he forgive us of our sins, but if we desire we can even lose the desire to ever commit the sin again. What a burden lifted off of our shoulders.
I know this to be true, there have been many weaknesses I have had in my life and many things I have struggled with. It was only through the atonement of my Savior, and repentance (Change) that I was able to be freed from these weaknesses. I have felt the true joy that can only come through Jesus Christ. I have truly experienced a "mighty change of heart"