Neros Shabbos Part 2

The Mishna Pesachim (53b) says that there were conflicting customs if one should light neros for Yom Kippur.  The Gemarah explains the machlokes according to Rashi's explanation that בין שאמרו להדליק - אותן שנהגו להדליק והנוהגין שלא להדליק לא נתכוונו אלא לדבר אחד להפריש עצמו ממשכבי אשה האומרים להדליק משום דאין אדם משמש מטתו לאור הנר והאומרים שלא להדליק סוברים כשהנר דולק רואה את אשתו ומתאווה לה.  The machlokes is about what is practically better to do to uphold the prohibitions of Yom Kippur.  The Gemarah continues that when Yom Kippur falls out on Shabbos, it is a machlokes if everyone agrees that one then lights candles, רַבִּי שִׁמְעוֹן בֶּן אֶלְעָזָר אוֹמֵר: יוֹם הַכִּפּוּרִים שֶׁחָל לִהְיוֹת בְּשַׁבָּת, אַף בְּמָקוֹם שֶׁאָמְרוּ שֶׁלֹּא לְהַדְלִיק — מַדְלִיקִין מִפְּנֵי כְּבוֹד הַשַּׁבָּת. וְעָנֵי רַבִּי יוֹחָנָן בָּתְרֵיהּ: וַחֲכָמִים אוֹסְרִים.  Presumably the Chachamam hold not to light for the same practical concerns as every Yom Kippur.  So why does רשב"א differentiate?  He would seem to hold that since Shabbos has an obligation of neros Shabbos, that applies even when Shabbos coincides with Yom Kippur.  In other words, he holds the practical concerns can't cancel out the obligation of neros Shabbos.  (The Chachamim disagree and hold even on Yom Kpput that falls out on Shabbos one should not light candles.  They may hold the practical concerns override the obligation of neros Shabbos or they hold when Shabbos coincided with Yom Kipput it is a hybrid kedusha and the Shabbos has the dinim of Yom Kippur and loses its own obligation of candles, ויש לעיין בזה.)  But why does he hold that a regular Yom Kippur doesn't have the same obligation?  It would seem to depend on the nature of the obligation of neros Shabbos.  In the post last week, 'Neros Shabbos,' it was brought up the issue is the mitzvah of neros Shabbos is for the candles to be lit on Shabbos or is the mitzvah to do an act of lighting the candles.  This debate may reflect what the reason of the mitzvah is.  If the mitzvah is to give kavod to Shabbos, then it is an act to be done before Shabbos for the sake of Shabbos, so it would be a mitzvah to light the candles but if the mitzvah is for oneg Shabbos because having a lit house enhances one's enjoyment of Shabbos, then it would suffice for the candles to be lit on Shabbos, one does not need to actively light for Shabbos.  Yom Kippur does have an obligation of kavod (Shabbos 119a) but does not carry the obligation of oneg.  It would seem רשב"א holds the obligation of lighting candles is in order to give oneg to the day and therefore, he holds a regular Yom Kippur does not have the obligation of lighting neros but Shabbos Yom Kippur does.  

The Rosh (Yoma Chapter 8 siman 27) however, says we always light a candle on Yom Kippur and say a beracha because of the mitzvah of shalom bayis.  He seems to be giving a third reason for the neros which is shalom bayis and that obligation applies even on Yom Kippur.  Rav Yosef Engel (ציונים לתורה כלל לח עמ' מז) is bothered that how can shalom bayis itself be a reason to light candles, if that is the case there should be an obligation to light a candle and one should say a beracha every single day of the year?  He says the Rosh must mean that due to the fact that there is kavod on Yom Kippur as well, one can say a beracha when lighting.  How does this fit in the words of the Rosh?  I assume he means that kavod is to do something is preparation for Shabbos that will enhance one's Shabbos experience.  In what way is one's Shabbos experience enhanced?  Because one's shalom bayis is enhanced that allows for a more enjoyable Shabbos. 

See more about this discussion in כוכבי יצחק siman 1.