Rashi on Numbers 8:19/רש"י על במדבר ח׳:י״ט

1ואתנה וגו׳ AND I HAVE GIVEN [THE LEVITES etc.] — Five times are the “children of Israel” mentioned in this verse (where the last four times they might have been alluded to by a personal pronoun), in order to show what affection they are held by the Lord in that the mention of them is repeated five times in one verse corresponding in number to the “Five Books of the Torah”. Thus I have seen stated in Genesis Rabbah (Leviticus Rabbah 2:4; cf. Genesis Rabbah 3:5).

2ולא יהיה בבני ישראל נגף [AND I HAVE GIVEN THE LEVITES … TO DO THE SERVICE OF THE CHILDREN OF ISRAEL] THAT THERE BE NO PLAGUE AMONG THE CHILDREN OF ISRAEL [WHEN THE CHILDREN OF ISRAEL COME NIGH UNTO THE SANCTUARY] — The meaning is: I have given them etc. so that it should be unnecessary for them to come near to the Sanctuary, because [having sinned by worshipping the Calf], if they came near there would be a plague among them.