Commentaire sur Les Nombres 29:18

ומנחתם ונסכיהם לפרים AND THEIR MEAL OFFERING AND THEIR DRINK OFFERINGS FOR THE BULLOCKS — The bullocks offered on the Feast of Tabernacles are seventy in all, in allusion to the seventy nations of the world, and they gradually decrease in number each day, an omen to them of gradual annihilation, but during the period when the Temple existed and these sacrifices were offered they protected them against this misfortune (cf. Sukkah 55b).

ולכבשים AND FOR THE LAMBS — in allusion to the Israelites who are called ( 50:17) “scattered lambs”. — They (the lambs) are of fixed number each day (a symbol that the Israelites are fixed, imperishable), and their total is ninety-eight, serving to avert from them the ninety-eight curses which are set forth in Deuteronomy (Deuteronomy 28:15 ff.) — In the paragraph dealing with the second day of the Festival, it is said, (v. 19) ונסכיהם, and this is in reference to the two daily continual offerings (while the usual term is ונסכה corresponding to ומנחתה that precedes it), and it sometimes uses a modification of the terms usually employed in those paragraphs only in order that some teaching may be deduced from it, as our Rabbis, may their memory be for a blessing, said: in the case of the second day we have ונסכיהם, of the sixth ונסכיה, of the seventh כמשפטם (instead of the usual כמשפטה): the additional letters are מ and י and מ — so you have here מים, “water”, — a suggestion that the libation of water on Tabernacles is of Biblical origin (מן התורה) (Sifrei Bamidbar 150; Shabbat 103b).