Yom Kippur is called Shabbat of the Shabbats, so maybe it is immaterial if Yom Kippur is also Shabbat. Well, apparently, it is not.
When Shabbat and Yom Kippur coincide, Sephardic Jews do Kabbalat Shabbat before Kol Nidre. Ashkenazic Jews who don’t say Avinu Malkenu on Shabbat or the day before Yom Kippur, then say it on Friday morning and close to the end of the Yom Kippur (basically after Shabbat). The Middle Blessing of the Main Prayer has many references to Shabbat and in fact contains and concludes with a Kiddush. After the morning Blessings and in the Middle of Mussaf, we mention the Shabbat Temple Sacrifice, and we add Shabbat to the Blessings we say over lighting Shabbat Yom Kippur candles. The number of Alliyot to the Torah reading goes from six (Yom Kippur) to seven (Shabbat) and the last Blessing on the Haftarah may mention Shabbat alone or together with Yom Kippur. And Ashkenazic Jews have an extra end-of-Shabbat Blessing in the Havdalah about smell. So we can’t say that Yom Kippur simply overrides Shabbat. (This unlike Rosh haShannah that almost completely eclipses (pun intended) Rosh Chodseh.) Shabbat stays on Yom Kippur.
(There is another rare instance of fasting on Shabbat – to help tear up an Heavenly terrible decree as indicated by certain nightmares – just as we try doing on Yom Kippur. Yet, Yom Kippur is not a (sad) Fast day; rather it’s a day so elevated that we don’t, couldn’t, can’t eat. On Yom Kippur we don’t fast – we only refrain from eating and drinking.)
But when they fall on the same day, more than Shabbat changes Yom Kippur, Yom Kippur changes Shabbat. We don’t: make Kiddush over a cup, eat three meals, sing table hymns or say blessings before or after eating (unless we must eat or drink for our health). That seems a pity.
Furthermore, there seems to be a real contradiction.
On Yom Kippur we are obligated to torment our Soul (Leviticus 16:29).
But on Shabbat we are obligated to enjoy ourselves (Isaiah 58:13-14). Normally that is done by having (and giving away) extra tasty meals.
How could we combine obligations to torment and enjoy ourselves?
Extra Soul Power
Maybe this can give an answer. On Shabbat we have an enlarged Soul (some say: extra Soul), but not on Yom Kippur, unless it’s also Shabbat. How can we know? The Shabbat Yom Kippur Ashkenazic Havdalah has this extra Blessing, meant to comfort us on the loss of extra Soul power that just took leave, which the weekday Yom Kippur Havdalah lacks.
Enhanced spirituality for Shabbat (Resh Lakish, Talmud, Beitza 16a, Rashi there explains) gives us: a heightened consciousness, repose, joy and tranquility, to respire (Exodus 31:17), and an ability to eat more without disgusting our Soul. It also enables extra Jewish learning (Rabbi Betzalel Ashkenazi). Perhaps we may say that just as (an?) extra Soul for Shabbat can help us feel great despite copious eating, just as well it could assist us on Yom Kippur to feel fantastic in spite of fasting.
In fact, when Yom Kippur is over (and the Evil Inclination doesn’t tell us anymore that we can’t take the fasting any longer, so that we now could go on without food and drinks for hours more), we often feel as if we had enormous meals on the Fast day. We feel delighted, cleansed and satisfied. We need to start eating slowly as if we were stuffed already.
So how do we do Oneg Shabbat when Yom Kippur coincides with it? We just do it through fasting helped by our Shabbat addition to our Soul. On a weekday Yom Kippur we come out feeling great too, but on a foodless Shabbat Yom Kippur we should come out bummed – but we don’t.
After Shabbat Yom Kippur just now, I asked a great Sephardic Rabbi how he was feeling. Fantastic. How come, I asked. And I answered my own question: Because just as the extra Soul on a regular Shabbat helps us to feel great despite an abundance of food, on a foodless Yom Kippur it helps us to feel great despite fasting. He replied: Great idea.
Another idea: My learning partner, Rabbi Yisrael, suggested that we’d smell herbs (with the Blessings) on Yom Kippur to help us enjoy Shabbat.
May all Jews and Gentiles (we prayed hard enough for them) all have a good and sweet year and many more to follow!