What are the connotations of the words "be'Etzem ha'Yom ha'Zeh"?
Ramban #1 and Moshav Zekenim: It means simply 'on this very day' 1 - to teach us that the day itself is intrinsically holy and atones, 2 irrespective of whether all the Korbanos and the Sa'ir ha'Mishtale'ach have been brought or not 3
Ramban #2 (citing the Sifra): When the Pasuk uses the term "be'Etzem ha'Yom ha'Zeh" in connection with the Yamim-Tovim, it means 'on this very day - from nightfall to nightfall', to preclude Tosefes Yom ha'Kipurim from Kareis 4 and from the Kedushah of Yom-Tov by Shavu'os. 5
See Ramban as to why it cannot mean 'in the middle of the day as in No'ach Bereishis, 7:13 and in Bo Sh'mos, 12:51. See also Ramban, DH 'u'Matzanu'.
"Ramban: And "be'Etzem" means the strength of the day - as if it would have written 'be'Otzem ha'Yom ha'Zeh'. See Ramban DH "ve'Chein Nir'eh li'.
Ramban: And the same explanation pertains to Shavu'os and to Chadash, where the Torah also inserts "be'Etzem ha'Yom ha'Zeh".
With regards to both eating and performing Melachah - Torah Temimah, citing Yoma, 81a. See notes 89 & 92. It is not clear as to why the Pasuk repeats the Chachamim make the same D'rashah with regard to the Chiyuv Kareis on Melachah. See Torah Temimah, citing Yoma, 81a and note 93.
Ramban: And by No'ach, Yetzi'as Mitzrayim and Moshe they explain it to mean 'in the middle of the day', as Rashi explains in Vezos ha'Berachah Devarim, (32:48) - Refer also to Bereishis, 7:13:1:1.
