Regret as the Root of Change

Rav Moshe teaches that regretting past sins helps us clarify our motive for changing. We want to better ourselves purely in order to fulfill Hashem's will, yet people may decide to stop sinning for far lesser reasons: they are no longer able to continue, they can no longer afford the lifestyle that includes the sin, or it no longer attracts them. The only way to be sure that our decision rests on Hashem's will is to feel regret over the fact that we did the sin.