Commentary for Numbers 28:4

את הכבש אחד THE ONE LAMB [SHALT THOU OFFER IN THE MORNING] — Although it has already been stated in the section beginning with the words ,ואתה תצוה (Exodus 29:38 39): “Now this is what thou shalt offer … [The one lamb thou shalt offer in the morning]”, that was an instruction for the days of the installation ceremony of the priests, but here it states the commands for all generations.

את הכבש אחד, “One of the lambs,” we would have expected the Torah to write את הכבש האחד, however the omission of the letter ה here is to alert us to the fact that the word אחד has a numerical value of 13 to teach us that 13 priests were involved in this procedure (Yuma 25). This number is also not accidental but is in itself a reminder that the offering was addressed to the אחד, to the One and Only G’d. In Exodus chapter 29,39 the Torah does write: את הכבש האחד, as is grammatically appropriate when speaking of an animal singled out from its flock as superior.

Here the commandment is for all the generations. (Kitzur Mizrochi) Ramban claims that this is not correct, for there it already stated, “A continual burned-offering for your generations.” Chizkuni answers that the minimum [meaning of the] number of “generations” is two and no more, therefore the verse where it is written “command” (v. 2) implies alacrity for now and for future generations is necessary.