1) COUNTING MONEY BY THE LIGHT OF THE CHANUKAH CANDLES
QUESTION: Rav Asi states that it is forbidden to count money by the light of the Chanukah candles. The Gemara earlier (21a-b) cites an argument whether or not it is permitted to derive benefit from the light of the Chanukah candles. Why does the Gemara here mention only that counting money is forbidden?
(a) The ROSH and TOSFOS (21a, DH u'Mutar) explain that Rav Asi is teaching that even counting money, which is a momentary activity and does not require much light, is forbidden to do by the lights of Chanukah. We might have thought that only using the lights for ongoing and involved activities is forbidden, but counting money is permitted. Rav Asi therefore teaches that there is a concept of Bizuy Mitzvah ("disgracing the Mitzvah") which prohibits doing any mundane activity by the light of the Chanukah candles. Rav Asi is more stringent than the earlier opinion that said it is forbidden to use the light of the Chanukah candles (for involved activities).
(b) The BA'AL HA'ME'OR explains that Rav Asi is actually more lenient than the earlier opinion. The earlier opinion that said it is forbidden to use the light meant that it may not be used for anything, even for a holy purpose, such as to perform another Mitzvah. Rav Asi maintains that it is forbidden to use the light only for mundane activities, but the might may be used for holy purposes, because there is no Bizuy Mitzvah in such a case.
The reason why the earlier opinion forbids the light to be used even for a holy purpose is because the Chanukah lights were instituted as a commemoration of the lights of the Menorah in the Beis ha'Mikdash. The lights of the Menorah were forbidden to be used for any other purpose, including purposes of holiness. Therefore, the Rabanan instituted a similar level of Kedushah for the lights of Chanukah and prohibited using them for any purpose.
(RASHI (21b, DH v'Asur) explains that the reason it is forbidden to use the lights is because there must be an indication that these lights were kindled for the sake of a Mitzvah, and by not using them one shows that they were kindled only for the sake of a Mitzvah. Rashi may understand, like the Ba'al ha'Me'or, that this opinion prohibits using the lights of Chanukah for any purpose. Rav Asi, on the other hand, does not require such an indication; he prohibits using the lights only because of Bizuy Mitzvah, and therefore using them for a holy purpose is permitted.)
2) HALACHAH: IS THE "KINDLING" THE MITZVAH, OR IS THE "PLACING" THE MITZVAH
QUESTION: The Gemara says that if a person lights his Chanukah Menorah inside his home and then he brings it outside, he does not fulfill the Mitzvah. The reason is either because the kindling is the Mitzvah ("Hadlakah Oseh Mitzvah"), and since he kindled it in a place that is not fit for the Mitzvah of lighting (inside his house), he does not fulfill the Mitzvah, or because the placing of the Chanukah Menorah is the Mitzvah ("Hanachah Oseh Mitzvah"), but someone who sees him bring the Menorah outside will think that he lit it inside for his own personal use and not for the sake of a Mitzvah.
The RIF, ROSH (2:7) and TUR (OC 675) rule that the kindling is the Mitzvah. They also rule that if one lights it inside and brings it outside, he does not fulfill the Mitzvah "because someone who sees him will think that he lit it for his own personal use."
Why do they give the reason of "someone who sees"? If they rule that the kindling is the Mitzvah, it is not necessary to give this reason! The kindling itself must be done in a place that is fit for the performance of the Mitzvah!
ANSWER: The BACH answers that although the reason of "someone who sees" is not really necessary, the Rif, Rosh, and Tur mention it because sometimes the first reason for why he does not fulfill his obligation (that the kindling must be done in a place that is fit for the Mitzvah) does not apply. For example, nowadays the accepted practice is to light indoors, and one thereby fulfills the Mitzvah. Accordingly, when one lights the Menorah inside and brings it outside, he has lit it in a place that is fit for the Mitzvah, and thus he should indeed fulfill his obligation even though he takes it outside. Therefore, they quote the second reason mentioned in the Gemara, that someone who sees might think that he lit the candles for his own personal use.
The authorities rule in accordance with the answer of the Bach; see MISHNAH BERURAH (OC 675:5). The Mishnah Berurah (apparently based on the words of the Vilna Ga'on there) adds that this Halachah also applies when a person lights the Chanukah Menorah outside and then brings it inside; the concern of "someone who sees" still applies (even though people do not usually kindle lights for personal use outside), and one does not fulfill the Mitzvah.