Kommentar zu Bamidbar 3:45

ואת בהמת הלוים וגו׳ AND [THOU SHALT TAKE] THE BEASTS OF THE LEVITES [INSTEAD OF ALL THE FIRSTBORN AMONG THE BEASTS OF THE CHILDREN OF ISRAEL] — The beasts of the Levites did not redeem the firstborn of the clean beasts belonging to the Israelites, but only the first offsprings of their asses (cf. Bekhorot 4a). One lamb of the Levites (it must be remembered that for the redemption of פטר חמור a lamb is prescribed; cf. Exodus 13:13) could, however, release several first offsprings of asses belonging to Israelites. You may know that this is so, for it (Scripture) mentions the number of firstborn Israelites in excess of the number of Levites in the case of human beings, but mentions no number of firstborn animals belonging to the Israelites as being in excess over the lambs of the Levites, [although there were undoubtedly many more firstborn asses of the Israelites than ordinary lambs of the Levites] (cf. Bekhorot 4b).

TAKE THE LEVITES INSTEAD OF ALL THE FIRSTBORN AMONG THE CHILDREN OF ISRAEL. The firstborns had become sanctified to G-d from the time that He commanded Sanctify unto Me all the firstborn … among the children of Israel etc.¹⁸¹Exodus 13:2. There were thus many firstborns in Israel who had not been redeemed until now, since it had not yet been said who would “redeem” them, for it was only now that the priests became sanctified, and [Israel] had not yet been commanded about the gifts of the priesthood.¹⁸²Further, 18:8-20. Thus they [the firstborns] continued without restriction in their sanctity, and it is possible that they performed the Service of the offerings, as our Rabbis have said.¹⁸³Zebachim 115 b.
The correct opinion appears to me to be that not all these firstborns were born in the desert in one year, for the people did not increase there so rapidly [that there should have been twenty-two thousand firstborns in one year, corresponding to the twenty-two thousand Levites, with an excess over the Levites of two hundred and seventy-three].¹⁸⁴Verse 46. Rather, all firstborns of Israel [alive at that time, even those born many years previously] were counted, for they were all sanctified, as I have explained there.¹⁸⁵Exodus 13:11. See my Hebrew commentary here p. 204. Now, He exchanged them for the Levites, and this was their “redemption,” and He commanded to redeem those that exceeded [the number of the Levites by means of each one giving five shekels]. And He gave the redemption-money to Aaron and his sons, as is the commandment for all generations [that a firstborn son be redeemed by giving five shekels to a priest].

והיו לי הלוים אני השם, "and the Levites will belong to Me I am the Lord." The reason the Torah added the words "I am the Lord," is to tell us that although according to Yalkut Shimoni 364 there will come a time when the firstborn will once again be performing the priestly functions in the Holy Temple, the Levites will not therefore be demoted and cease to belong to G'd. [I have not foumd a reference in the Yalkut to the firstborn being reinstated as priests in the future. Ed.] The very expression והיו לי indicates that just as G'd's name is eternal so is the appointment of the Levites to their task.

תחת כל בכור בבני ישראל, “in place of every firstborn of the Children of Israel.” According to Nachmanides the firstborn males of Israel had attained the status of being sanctified ever since Exodus 13,2 when G’d had told Moses to sanctify the firstborn to Him, seeing that He had not killed the Jewish firstborn when the Egyptian firstborn had been slain. There were in the meantime very many firstborn who had never been redeemed, as up until now it had not been revealed to whom the money for redeeming them was to be given. They were therefore in a state of arrested sanctity, unable to all perform priestly duties, and unable to lead ordinary lives. It is possible, as argued by our sages, that some of them had performed as priests. Nachmanides adds, that as far as he personally is concerned, it is most unlikely that all these 22000 firstborns had been born during the year that had elapsed since the Exodus, as we have no reason to believe that the people had multiplied at such a rapid rate since they had been in the desert. The count included all the firstborn, including the many who had been born prior to the Exodus. All of them were redeemed now for the Levites. The 273 for whom no matching Levites could be found, were redeemed for 5 shekels each, the money being given to Aaron and his sons, as became the law for all subsequent generations.

But [they did redeem] the firstlings of their donkeys. There are those who explain that Rashi is answering the question: If the verse refers to kosher animals it would not be possible to redeem them, because the sanctity of a firstborn would not be released given that the kohanim themselves were obligated regarding the sanctity of the first animals. One may say further that Rashi’s proof is from Parshas Bo where it is written “and every firstling donkey you shall redeem with a sheep… and every firstborn man you shall redeem” (Shemos 13:13), thus here it also refers to [the redemption of a firstborn man, and] the firstborn animal, refers solely to the firstling donkeys. (Re’m) This is puzzling: Surely Rashi himself explains differently in the first chapter of Bechoros (4a), concerning Rava’s challenge to Abaye. [Rava says:] If you are correct, that one can learn a kal vachomer (a fortiori reasoning) from the case of an animal then the Levites should be exempt from the redemption of firstborn kosher animals! [Since the Levites’ kosher animals are not exempt, Abaye’s kal vachomer must also be false.] – [there Rashi explains:] because their kosher animals released the kosher animals of the Israelites. The matter requires investigation. However perhaps the answer is that the challenge made by Rava upon Abaye was only according his own reasoning, however Abaye disagrees and holds that the animals of the Levites did not redeem the kosher firstborn animals of the Israelites. See Minchas Yehudah.

קח את הלוים תחת כל בכור בבני ישראל, “take the Levites in exchange for all the firstborn of the remainder of the tribes of Israel.” The reason why the Levites alive now were not used to also redeem the Israelites that were to be born during the 38+years that the Israelites were still to wander through the desert, is because the Levites that were sanctified now had already been born by other Levites who had redeemed firstborns. It is not logical to assume that they possessed the spiritual power to redeem a second time. All the firstborns that are mentioned at this point were not the ones that had been redeemed by Levites in the desert, but had been born by ordinary Israelites who had never been redeemed; the firstborns that had been redeemed by Levites had not been known to also redeem as yet unborn firstborn that stemmed from them.

But did not count the extra animals. (Re’m) It is puzzling how he brought this proof which the Talmud (Bechoros 4b) had already negated? The Talmud [disproved this by saying] that perhaps the [Levites] had many animals which were equal in number to the firstborn [animals] of the Israelites. [The Talmud] brings another proof: The verse says ואת בהמת הלוים תחת בהמתם (lit. and the animal of the Levites instead of the Israelites’ animals) implying that one animal was in place of many. Because if you would think that ואת בהמת הלוים refers to many animals, then the verse should have either written בהמת both times or בהמתם both times. [However since it changed its language,] we see that one animal exempted many. He answers that Rashi discarded the second proof because it was far from the simple reading of the verse, and therefore he brought the first proof.