By other leftover tashmishay mitzvah [items used to fulfill a mitzvah] items, we don’t find that there is a special din [law] that the item must be burnt, so why is that by leftover Chanukah candles we do find such a din?
The Ran (Shabbos, 9a MiDafay HaRif) asks, why leftover Chanukah oil is different to wood that was used for building a succah and leftover succah decorations where we don’t find a din that they must be burnt? He answers, that when one builds a succah he aspects to have wood and decorations leftover after Succos, therefore, he doesn’t fully take his mind off them, therefore, they don’t become forbidden to benefit from. When it comes to Chanukah candles, however, one expects that oil and the wicks will get burnt up, therefore, when one lights them, he takes his mind off them completely, consequently, they become הוקצה למצוותו, set aside for the mitzvah.
The Avudraham (Seder Chanukah) adds, that Chazal treated leftover Chanukah oil like tashmishay kedusha, as the leftover Chanukah oil is a zecher [remembrance] to the leftover oil that was used in the Beis HaMikdosh. According to the first reason we mentioned, it’s difficult to understand why leftover Chanukah candles needs burning, whereas leftover Shabbos candles doesn’t?
The Ran addresses this issue as well, and he answers, that there is a difference between Shabbos candles which one is allowed to benefit from, and Chanukah candles which one isn’t. Since one is allowed to benefit from Shabbos candles, one isn’t required to burn the leftover oil.
Tashmishay kedusha, refers to items such as tefillin and sifrei Torah, which one must treat with more respect than tashmishay mitzvah, and one isn’t allowed to just throw them in the garbage.
The Ran also mentions a Tosfos in Shabbos (44a) which differentiates between Chanukah and Shabbos candles. Tosfos says, Chanukah candles come for pirsumay nisa and not for one’s personal benefit, and due to the love for the miracle (חביבות הנס) one doesn’t wait for the candles to go out, on the contrary, he wants all the oil to get used up for the mitzvah. Shabbos candles, however, are lit for one’s personal benefit, and once one no longer needs them, he ideally wants them to be extinguished so he can have leftover oil, therefore, any leftovers are permissible.
