Repentance is the second princple of the gospel, just after faith as stated in the fourth article of faith. Repentance is closely tied to the atonement. The atonement of Christ makes repentance possible.
The Lord "commandeth all men everywhere to repent, D&C 133:16. In addition to it being a commandment to repent, it is also an invitation to partake of the tree of life, Alma 5:32-36.
The effects of King Benjamin's speach was that the people had a change of heart, Mosiah 5:2. Alma also talks of the mighty change of heart that is needed, Alma 5:13-15. This change of heart is not necessarily permanent, we have to keep working at it in the same way as we originally received it, Alma 5:26.
Isaiah teaches us about repentance. He says: "Wash you, make you clean," Isaiah 1:16. "though your sins be as scarlet, they shall be as white as snow," Isaiah 1:18. "God, for he will abundantly pardon." Isaiah 55:6-7. In the Old Testiment the word repent is ofted used to mean a simple change of mind. For example see Psalms 38:18 where it talks about the Lord changing His mind or repenting. Of course the Lord already knew what he was going to do, but he is talking unto man as if he had changed his mind.
John the Baptist taught "Repent ye: for the kingdom of heaven is at hand," Matthew 3:1-2 and "Bring forth therefore fruits worthy of repentance," Luke 3:7-8.
We need to repent so we won't have to suffer what Christ suffered for us, D&C 19:15-20.
After the jews were brought back to Jerusalem, Ezra read the law to them and they confessed their sins and worshiped God, Nehemiah 9:1-3.
We need to confess and forsake our sins, Proverbs 28:13, Psalms 38:18, and D&C 58:42.
The parable of the lost sheep shows how much joy there is over the return of one lost sheep to the fold, Luke 15:3-7.
"fear not, and lay aside every sin, which easily doth beset you," Alma 7:14-15.
When we repent, the Lord remembers our sins no more, D&C 58:42-43.
This life is the time to prepare to meet God, Alma 34:32.
There are too many ways to commit sin to number them all, Mosiah 4:29-30.
The parable of the Prodigal Son is an example of how we should treat the repentent sinner, Luke 15:11-32. The father never gives up on his son, no mater how far he strayed. It can be difficult to accept the repentent sinner back. It seems like they are getting a free ride. However, we need to rejoice with them instead of judge them. Unlike in the parable where there is only one estate to give, we all enherit all that the Father has.
All men need to be changed from their carnal state, to a state of righteousness, Mosiah 27:24-26.
In Alma's day there was great iniquity a pride in the Church requiring great repentance, Alma 5:7-15.
Everyone must repent and be baptized, Alma 5:49.