Commentary for Numbers 29:35

עצרת תהיה לכם ON THE EIGHTH DAY THERE SHALL BE A עצרת (RESTRICTION) FOR YOU — you are restricted in the doing of work. Another explanation of עצרת: Restrict yourselves from leaving Jerusalem: this teaches that this (the eighth day) requires that they should remain in Jerusalem overnight (that the pilgrims should not immediately at the termination of the seventh day begin their homeward journey) (Sifrei Bamidbar 151:1). And an explanation of it in the Agada is: because on all the seven days of the Festival they offered sacrifices corresponding in number to the seventy nations of the world, and they propose then to set forth on their way home, the Omnipresent says to them: ‘I beg of you make a small banquet for Me, so that I may have some pleasure from you exclusively” (Sukkah 55b).

Restraint from doing work. Thus, when it is written afterwards, “You shall not do any work of substance” this is an additional explanation, [meaning] that the verse itself explains what you shall restrain yourselves from.