go here Mai Nafka-Minah?
[20b middle] Gemarah discusses about doing http://relglaw.com/plus/download.php?open=1 Kriah (ripping clothes for a deceased relative) after Shabbos. Ran (quoting Yerushalmi in GM’ Shabbos): If did Kriah on Shabbos, it is valid (even though one certainly gets an Aveirah). The concept of Mitzvah Haba’a B’aveira (a good deed brought about through a prohibition) applies by a stolen Matzah (and therefore one does not even fulfill his obligation), but why not by ripping Kriah on Shabbos as well (why do you still get credit here)? The “Nafka-Minah” (practical difference) between these two cases is an issue of Cheftza (thing) / Gavra (person). Matza is a stolen ITEM and therefore object itself becomes disqualified from doing a Mitzvah with it. However by Kriah, the person just happens to be getting an Aveirah (nothing becomes disqualified, the object is no different than before) and the clothing has the Mitzvah attached to it.
enter E’s Lesson: Items (Cheftzos) can become permanently disqualified and unable to ever have Mitzvos performed with them again [some items like earthenware vessels must be smashed if they contract impurity]. However, when a person (Gavra) sins (or becomes disqualified) he/she always has the potential to become requalified again. We can always do Teshuva. May we keep this message now in mind during Elul and utilize every opportunity we have to fix our Gavra and use our all Cheftzos for Mitzvah related purposes.