Or HaChaim on Deuteronomy 32:48/אור החיים על דברים ל״ב:מ״ח

1 בעצם היום הזה לאמור. "on that very day, saying." Moses was to tell the people that he would ascend the mountain in order to die. This corresponds to what Sifri explains on the word בעצם that on the three occasions when this word appears it reflects G'd's determination not to be interfered with. In this instance the Israelites had threatened to physically prevent Moses from ascending the mountain to die there.