What is the significance of the seven bulls and the seven sheep on seven Mizb'chos?
Ramban (citing Ibn Ezra 1 ): 'The number even is prominent in the days of the week, in the months and in the years; in the seven lambs of the Olah (of most Musaf offerings) and the seven sprinklings (on Yom Kipur). Also Iyov was told to bring seven bulls and seven rams. 2
Ba'al ha'Turim: It was customary for gentiles to bring seven of each species as sacrifices, 3 corresponding to the seven Mitzvos b'nei No'ach.