All people are born with the capacity to distinguish between right and wrong. This ability, called conscience, is a manifestation of the Light of Christ (see Moroni 7:15–19). A person's conscience is a defense against situations that are spiritually harmful.
Righteous decisions and obedience to the commandments bring peace of conscience.
When we sin, we feel remorse or guilt, just as we feel physical pain when we are wounded. This is the natural response of our conscience to sin, and it can lead us to repent.
Repentance and forgiveness renew our peace of conscience. On the other hand, if we ignore our conscience and do not repent, our conscience will be impaired as if it has been “seared with a hot iron” (1 Timothy 4:2).
We are to learn to follow our conscience. This is an important part of exercising our agency. The more we follow our conscience, the stronger it will become. A sensitive conscience is a sign of a healthy spirit.
—See True to the Faith (2004), 40
From an address given on June 22, 2004, at a seminar for new mission presidents, Missionary Training Center, Provo, Utah. What Everyone Called to Preach the Gospel, Teach the Gospel, or Live the Gospel Should Know
For many, relief and happiness can come by understanding the relationship between peace of conscience and peace of mind.