Also: Remorse, Contrition, Shame
Repentance is feeling shame and seeking to make amends when we have done something wrong. When we repent, we turn away from old behaviors and commit ourselves to better ones.
Without remorse or repentance, many kinds of growth are impossible. Unless we can see our errors and the harm done--and regret both--we are doomed to repeat them. And yet, repentance need not include self-flagilation or loathing; it is the former behaviors or attitudes that we eschew. When we get overly focused on self-criticism, we have less energy available to repair the harm we have caused.
Repentance is easier when we recognize that everyone does things that are ugly, which is why we all cherish understanding and grace.