Komentarz do Liczb 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.