Kommentar zu Bamidbar 8:18

ואקח את הלוים תחת כל בכור, a regulation applicable only during the generation addressed by Moses at the time, a one-time procedure, as we explained previously.

ואקח את הלוים, “I shall take the Levites, etc.” Ibn Ezra comments that in spite of the fact that G’d had already said (past tense) לקחתי אותם לי, “I have taken them for Me,” (8,16) it is the style of the Torah to repeat what had been said before if an interruption had occurred in the interval, one that interferes with one’s trend of thought. (Verse 17 which provides historical background) The Torah is saying that as soon as the Levites had been singled out by G’d, He handed them over for instruction in their duties by the priests.

ואקח את הלוים תחת כל בכור, “I have taken the Levites instead of the firstborn.” If all the firstborn were to perform service in the Temple, this would lead to the people suffering a plague, as there was no guarantee that the father of the firstborn performing that service had also been a firstborn, neither his grandfather. As a result, that family had not had an opportunity to become thoroughly familiar with all the intricacies of Temple service. Failure to perform the service properly would result in G-d’s killing such a person as we know from what happened to the two older sons of Aaron, Nadav and Avihu. Once the Levites had been appointed and the status had become a hereditary one, each member of each family made a point of being thoroughly familiar with all their duties. This is why the Torah writes: 'לא יהיה ללוי חלק ונחלה וגו, “the Levite is not to own ancestral land in the lad of Israel;” (Deuteronomy 18,1) by not owning land and growing crops they were free to concentrate on their tasks as Levites. They should not acquire too much familiarity with the tools used by farmers and artisans, so that they would not be diverted from their principal vocation, service in the Temple. If the Levite were to devote himself to those mundane activities, his fingers would become too coarse to play the musical instruments efficiently to accompany the choir of Levites during the time when Temple service was in progress.

לעבוד את עבודת בני ישראל, “to perform the service of the Children of Israel (collectively), which basically had been the task of the firstborn of each family in each tribe.

ולא יהיה בבני ישראל נגף, “and the there will not be a plague among the Children of Israel,” even a single one of them. We can find similar constructions in Exodus 21,11: ואם שלש אלה לא יעשה לה, “and if (her master) does not do one of these three economically constructive actions for her, etc.” (Exodus 21,11) Compare also Judges 12,7, “he was buried in the towns of the region of Gilead.” [All the people of surrounding towns took part in Yiftach’s burial. Ed.]