Or HaChaim on Numbers 8:19/אור החיים על במדבר ח׳:י״ט

1 ואתנה את הלוים נתנים לאהרון ולבניו, "and I have given the Levites,-they are given to Aaron and his sons, etc;" why did the Torah repeat the word נתנים, "they are given?" This may be intended to obligate the recipient of a gift to accept that gift and not to refuse it. Although in matters of inter-personal relationships it is perfectly in order for a person to decline to accept a gift as long as it has not come into his possession (his hands) and he has thereby acquired it, in this instance the Torah obligates the priests to accept this gift although acceptance involves negative aspects. By accepting the new status of the Levites -even though they were subordinate to the priests- the kind of duties performed by the priests became forbidden to the priests on pain of death. This is the view of Sifri on Numbers 18,3. The wording there is: "both they and you will be subject to the death penalty; you when you interfere in matters allocated to them and they when they interfere in matters allocated to you." This contrasts somewhat with what Maimonides wrote in chapter 3 of Hilchot Kley Hamikdosh where he describes Levites who performed service in the Temple, i.e. the domain of the priests, as guilty of death at the hands of Heaven. However, he describes priests who perform tasks allocated to the Levites as guilty of transgressing only an ordinary negative commandment, and not guilty of death. At any rate, Maimonides also agrees that such a transgression on the part of the priests qualifies for some retribution. Considering this we could understand why the priests would decline the gift of the Levites. The Torah therefore had good reason to repeat the word נתנים to deny the priests the option to decline this gift.

2מתוך בני ישראל, from among the children of Israel, etc. Our verse repeats the expression בני ישראל five times, apparently without reason. Our sages in Vayikra Rabbah 2,1 consider mention of that word an expression of G'd's fondness for the Jewish people. The five-fold mention corresponds to the five books of the Torah. This is all homiletics, of course. According to the plain meaning of the verse the number of times the children of Israel are mentioned appears absolutely justified. When the Torah writes מתוך בני ישראל, it refers to the Jewish people as long as these included the tribe of Levi on an equal footing. When it referred to the עבודת בני ישראל this is a reference to the firstborn of the Israelites who had performed the priestly functions up until then. The Levites had now taken over their functions. The Torah had to refer to these firstborns as בני ישראל instead of merely writing עבודתם, "their service," seeing it was no longer "their service." When our verse continues with the expression לכפר על בני ישראל, it refers to a description of the entire Jewish people. The reason the Torah did not choose the shorter לכפר עליהם is that this would have sounded as if it referred to the people mentioned or rather referred to last, i.e. the firstborn. When the Torah continues with ולא יהיה בבני ישראל נגף instead of ולא יהיה בהם נגף, it does so in order that we should not understand that the absence of such a plague is merely the result of the atonement mentioned previously. The Torah speaks of two separate benefits devolving on the Israelites as a result of the Levites performing their tasks. 1) There will be no mental illness due to sins perpetrated for which the Levites attain atonement. 2) There will be no physical plague which would result through the unauthorised entry of the Israelites into the sacred precincts of the Tabernacle. It makes eminent sense that this is what the Torah has in mind here as the message is not related to what had been discussed previously. When the Torah continues with בגשת בני ישראל, it means that even though only individuals might become guilty of violating these sacred precincts, the ramifications of the sin of these individuals would involve the whole people. G'd's anger would be vented at the people as a whole. We know from the uprising of Korach which involved only a few people, that Moses had to remonstrate with G'd when he noticed that G'd held the entire nation responsible (compare Numbers 16,21-22).