בעצם היום הזה, "on this very day.⁠" Nachmanides writes that the commentators generally understand the word בעצם as meaning "the substance of this day.⁠" It would have that same meaning in verse 14 of our chapter ולחם וקלי וכרמל לא תאכלו עד עצם היום הזה, "you must not eat either bread, parched kernels or roasted kernels (from the new harvest) until this very day.⁠" The word עצם does not appear in connection with the Sabbath day, or in connection with any of the festivals. It is only featured in connection with the festival of Shavuot and the Day of Atonement. The reason may be that just as the prohibition of eating from the new barley crop before the omer offering had been presented on the day itself, not the previous evening, it is parallel to the count which is to conclude 50 days after the time when the omer offering has been presented, when the new wheat harvest may be used for an offering. We might have thought that the various commandments attached to either the Day of Atonement or the festival of Shavuot are inextricably linked to the offering of the sacrifices the Torah tells us to offer on those days. By adding the rider בעצם היום הזה, the Torah teaches that each commandment in connection with these special days is standing on its own and has to be observed because of the date on which this day occurs, not because some other auxiliary commandments connected with these days. The word בעצם היום also implies that the night of the day in question is included in the special regulations pertaining to this day, unless of course, specifically excluded. Nachmanides adds that the word עצם is closely related to expressions denoting strength, toughness, etc., as in כחי ועוצם ידי, "my own power and the strength of my hand, [as opposed to God's] Deut. 8,17). Another example is עוז ותעצומות לעם, Psalms Seeing that what supports the body is a certain toughness of character, attitude, etc., the Torah uses the expression עצם היום as in the "skeleton" of the day, the essence of it, when the occasion warrants it.