Issur Melacha and Issur Achila On Yom Kippur

I saw an interesting chiddush in the Mesoros HaRav Machzor, the new machzor just published that contains the torah thoughts of Rav Soloveitchik about Yom Kippur.

The Rav writes that we find in the piyutim that Rabbi Eliezer HaKalir refers to Yom Kippur by three names: a)Yom Kippurim b) Tzom HaAsiri c) Shabbas Shabboson. However, the Rambam in Hil Shivisas Asar only refers to two names a) Yom Kippurim b) Shivisas Asar. The Rambam seems to fuse the names Tzom HaAsiri and Shabbas Shabboson into one name. The Rav explains that the machlokes between Rav Eliezer HaKalir and the Rambam is how to understand the nature of the issur of eating and drinking on Yom Kippur. The Rambam holds that it falls under the same issur as doing melacha. Therefore, he fuses the name Tzom HaAsiri which represents the issur achila with the name Shabbas Shabboson which represents the issur melacha.

Interestingly (although not surprising) , Rav Shirkin in Harirei Kedem (Siman 49) says the exact same thing although he doesn't bring it as a machlokes between the Rambam and Rabbi Eliezer HaKalir and he doesn't mention the point of calling Yom Kippur, Tzom HaAsiri. Also, Rav Shirkin writes that the Rav heard this idea either from Rav Chaim or Rav Moshe Soloveitchik. The way Rav Shirkin brings it is that the issur achila comes from the same kedushas hayom as the issur melacha.

The rayah to this comes from the Rambam in Hil Avodas Yom Kippurim (3:7). The Rambam writes that the shaliach responsible for taking the Azazael to the midbar can eat if he feels weak. The Rambam is mashma that we don't require that the shalaich be in a matzav of pikuach nefesh, but only that he feels weak. How does the Rambam know this? Based on the above yesod, we can understand this halacha. The issur achila of Yom Kippur comes from the same kedushas hayom as the issur melacha. Therefore, just like you can do melacha for the avodas hayom, you can also eat to enable you to complete the avodas hayom.

The above rayah is found in both the machzor and in Harirei Kedem. Rav Shirkin adds in another rayah from the fact that the Rambam writes (Shevisas Asar 1:5) that the mitzva to refrain from eating and drinking comes from the possuk "shabbos shabboson". The mitzvah of shabbson implies a mitzvah to keep the kedushas hayom and the same kedushas hayom that assurs melacha also assurs eating and drinking. Therefore, we can learn out issur achilah from "shabbos shabboson"