We all do things we regret, that conflict with our morality. Guilt is the result. Those actions cannot be undone, so it is necessary to find a way to make amends. It is astoundingly easier to merely ask for forgiveness from the Lord, which is bound to be received. The sin is instantly remitted. You are satisfied from an spiritual perspective.
Without a similar ideology, a person is forced to rationalize their negative feelings away. That is much more difficult.