Yechezkel Perek 33
In 33:12 Yechezkel states that a righteous person who discards his religious observance will not be rewarded for his mitzvos. Rashi, (3:20) explains that this concept refers to one who regretted his mitzvos. Additionally, Yechezkel adds that a wicked person who repents will be rewarded for his mitzvos. How does this apply to the concept of teshuva?
Teshuva is a huge chesed from Hashem that allows us to undo any previous misdeeds via simply regretting, comitting not to re-sin and confessing. It is an unnatural opportunity given to us by Hashem out of pure chesed/rachamim, as the Mesilas Yesharim states in perek 4. However, we find that the same concept applies in reverse to our mitzvos; if one regrets having performed a mitzvah then one gets no reward for it. This would imply that there is a natural phenomenon whereby once one regrets a deed, that deed is no longer a part of him. This understanding of teshuva does not fit with the Mesilas Yesharim’s description of teshuva as a unique kindness.
We will suggest three approaches:
When one does teshuva for a sin, it is natural that Hashem eliminates the aspect of transgressing the Divine will, for as when one regrets performing a mitzvah, one has changed the willingness to listen to or rebel against Hashem. But if one regrets a mitzvah, there is no way to take away the spiritual fact that he has received the benefit of the mitzvah. The miraculous aspect of teshuva is that regarding sins, Hashem will cancel out the negative spiritual repercussions for one’s actions.