Numbers 4:49

And they were counted, as Adonoy commanded Moshe. Those counted were, as commanded, from the ages of thirty to fifty.

By the mouth of the Word of the Lord were they numbered by Mosheh, every man according to his service and burden; and the numbering of them was as the Lord commanded Mosheh.

UPHKUDAV’ (THUS WERE THEY NUMBERED OF HIM) ‘ASHER’ THE ETERNAL COMMANDED MOSES. “A Masorah is the tradition handed down from generation to generation of the exact Scriptural text, and also refers to a collection of exegetical notes on the Scriptural text. The comment before us is of this second class. has it: Five [words in the Scriptures] are written asher (‘which,’ or ‘that’) but they are to be understood as ka’asher (‘as’), literally meaning: [and his countings] “which the Eternal commanded,” and Rashi on the basis of a Masorah interpreted it to mean: ka’asher tziva Hashem — [thus were they numbered] “‘as’ the Eternal commanded.” Ramban later on interprets the text asher tziva Hashem in its literal meaning. [this being one of the five cases, and therefore the above expression is to be interpreted as follows: thus were they numbered of him ‘as’ the Eternal commanded Moses]. And those counted were, in accordance with the command, from thirty to fifty years old.” This is Rashi’s language. If this is so, the word, uphkudav refers to Moses [thus were they numbered ‘of him’ — by Moses]. But Rabbi Abraham ibn Ezra commented that [the meaning of the verse is as follows]: every one, that is to say, of the three [Levitical] families — namely, Gershon, Kohath, and Merari — Moses appointed to his service, and to his burden as Scripture mentioned above [that he should appoint them]. And this is the meaning of [the word] uphkudav, namely “[the appointment] of every one” mentioned.
But it is possible that the expression ‘asher’ tziva be understood in its plain sense [i.e., “which” He commanded, and not, as Rashi has it, as if it said ‘ka’asher’ tziva — “as” He commanded]. Scripture would thus be saying that Moses appointed [each of the sons of] these three brothers [i.e., Gershon, Kohath, and Merari] to his service and to his burden as explained above; ‘uphkudav’ (and the numbered individuals) of each of them ‘which’ the Eternal commanded Moses to count by their polls, he appointed to his service, and to his burden. Thus the verse mentioned that Moses numbered them by their families, and also that he appointed the [numbered] individuals by their polls, every one to his service, and to his burden. is to be understood as ka’asher tziva (“as” the Eternal commanded). b) Rashi explains uphkudav as meaning “his countings,” i.e., those of Moses. Ibn Ezra interprets it as “his appointments,” the pronoun “his” referring to each of the three Levitical families. c) Ramban explains asher tziva in its literal sense, “which” the Eternal commanded [as explained in the text], the word uphkudav he understands as does Rashi, i.e., as “countings,” but the pronoun [“his”] Ramban explains as referring to each of the three brothers [Gershon, Kohath, and Merari — not personally, but in the sense of the descendants of each of them] ‘which G-d commanded’ Moses to count by their polls — each of them he assigned to his individual work. And such indeed is the law, that a Levite [of one group] is not permitted to do the work of another group or to assist therein, just as the Rabbis have said: “It once happened that Rabbi Yehoshua the son of Chananyah wanted to help [his fellow-Levite] Rabbi Yochanan the son of Gudgada to close the gates [of the Sanctuary]; whereupon [the latter] said to him: ‘Turn back, [for if you do not do so] your life is already forfeit, since I am one of the gatekeepers, and you are one of the singers.’”

EACH ONE TO HIS WORK AND HIS PORTERAGE AND HIS RESPONSIBILITY. He appointed each one to the work that he would do at the time of encampment AND HIS PORTERAGE at the time of traveling, that he would know the weight of his burden and he would know his responsibility, i.e., that he would know the names of the names of the items that he would carry that were designated by name, as it is said (v.32), "you shall list by name the objects that are their porterage tasks."