Another interpretation (of Numb. 3:40), “enroll every first-born male.” This text is related (to Cant. 6:8-9), “There are sixty queens, eighty concubines, and maidens without number; [but only] One is My dove, My perfect one….” [The matter] is comparable to a certain merchant, who had glass beads, which he would bring to market; but he paid no attention to their number (minyan), because he had brought them out without counting (minyan) [them]. So when he came in to put them away, he put them away without counting. Because they were [made] of glass, he did not pay attention to them. However, he had a certain string of fine pearls; and this he would take and bring out with a count, then put away with a count.
Similarly, as it were, the Holy One, blessed be He, said [in regard] to the nations of the world, “I have not given them a count, because none of them is important to me, as stated (in Is. 40:17), ‘All the nations are as nothing before Him; they are considered by Him as less than nothing and void.’ But as for you, you are My children, [as stated (in Is. 46:3)], ‘the ones who have been borne by Me from birth, carried from the womb.’
I therefore count you on every occasion.” It is therefore stated (in Numb. 3:40), “enroll every first-born male.” Ergo (in Cant. 6:8-9), “There are sixty queens […]; [but only] One is My dove, My perfect one….” This is Israel.
Another interpretation (of Numb. 3:40), “enroll every first-born male.” The Holy One, blessed be He, said, “Because of the love for Israel I have altered the [natural] order of the world. How? I had written in My Torah that an ass should be redeemed with a lamb, as stated (in Exod. 34:20), “But the firstling of an ass you shall redeem with a lamb (seh) ….”
But I did not do so. Instead I redeemed a lamb (seh) with an ass. The Egyptians are likened to an ass, where it is stated (in Ezek. 23:20), “whose flesh is like the flesh of asses”; and Israel is called a lamb (seh), where it is stated (in Jer. 50:17), “Israel is a scattered flock (seh).” Then I slew the first-born of the Egyptians and sanctified the first-born of Israel, as stated (in Numb. 3:13), “For every first-born belongs to Me on the day that I smote all the first-born in the land of Egypt,” I sanctified them for Myself. He therefore said to him (in Numb. 3:40), “enroll every first-born male among the Children of Israel.”