במדבר ג׳:ה׳-י׳

ושרתו אתו. וּמַהוּ הַשֵּׁרוּת?

And they shall serve him. What is the service? [The next passage explains —] ”They shall preserve his guardianship;” since he (Aharon) is obligated to guard the Sanctuary so that no stranger may approach, as it is said, “. . . you (Aharon), your sons, and your father’s house with you shall bear [responsibility for] the sin of [defiling] the Sanctuary . . .,” and these Levites aided them, this is the service.

ושמרו את משמרתו. לְפִי שֶׁשְּׁמִירַת הַמִּקְדָּשׁ עָלָיו שֶׁלֹּא יִקְרַב זָר, כְּמוֹ שֶׁנֶּאֱמַר "אַתָּה וּבָנֶיךָ וּבֵית אָבִיךָ אִתָּךְ תִּשְׂאוּ אֶת עֲוֹן הַמִּקְדָּשׁ" (במדבר י"ח), וְהַלְוִיִּם הַלָּלוּ מְסַיְּעִין אוֹתָם, זוֹ הִיא הַשֵּׁרוּת:

ושמרו את משמרתו. כָּל מִנּוּי שֶׁהָאָדָם מְמֻנֶּה עָלָיו וּמֻטָּל עָלָיו לַעֲשׂוֹתוֹ קָרוּי מִשְׁמֶרֶת בְּכָל הַמִּקְרָא וּבִלְשׁוֹן הַמִּשְׁנָה, כְּמוֹ שֶׁאָמוּר בְּבִגְתָן וָתֶרֶשׁ "וַהֲלֹא אֵין מִשְׁמַרְתִּי וּמִשְׁמַרְתְּךָ שָׁוָה" (מגילה י"ג), וְכֵן מִשְׁמְרוֹת כְהֻנָּה וּלְוִיָּה:

They shall take care to preserve his guardianship. Any position to which a person is appointed which requires his active management is called a “watch” throughout Scripture, and in the Mishnaic idiom, as stated concerning Bigsan and Seresh, “But surely my watch is not similar to yours”? Similarly, the “watches” of the kohanim and Levites.

ואת משמרת בני ישראל. שֶׁכֻּלָּן הָיוּ זְקוּקִין לְצָרְכֵי הַמִּקְדָּשׁ, אֶלָּא שֶׁהַלְוִיִּם בָּאִים תַּחְתֵּיהֶם בִּשְׁלִיחוּתָם, לְפִיכָךְ לוֹקְחִים מֵהֶם הַמַּעַשְׂרוֹת בִּשְׂכָרָן, שֶׁנֶּאֱמַר "כִּי שָׂכָר הוּא לָכֶם חֵלֶף עֲבֹדַתְכֶם" (במדבר י"ח):

And the watch of Bnei Yisroel. They were all actually obligated to provide the needs of the Sanctuary; the Levites merely served in their place, as surrogates. This is why they (the Levites) accepted the tithes from them, in payment, as it is said, “. . . for it (the tithe) is your payment, in return for your service . . .”

נתונם המה לו. לְעֶזְרָה:

They are presented to him. For assistance.

מאת בני ישראל. כְּמוֹ מִתּוֹךְ בְּנֵי יִשׂרָאֵל, כְּלוֹמַר מִשְּׁאָר כָּל הָעֵדָה נִבְדְּלוּ לְכָךְ בִּגְזֵרַת הַמָּקוֹם וְהוּא נְתָנָם לוֹ, שֶׁנֶּאֱמַר "וָאֶתְּנָה אֶת הַלְוִיִּם נְתֻנִים" וְגוֹ' (במדבר ח'):

From [among] Bnei Yisroel This [מֵאֵת, “from”] is understood as מִתּוֹךְ, “from among” Bnei Yisroel, meaning from the rest of the entire congregation they (the Levites) were selected for this by Divine decree and He (God) gave them to him (Aharon), as it is said, “I (God) have given the Levites, given [them] . . .”

ואת אהרן ואת בניו תפקד. לְשׁוֹן פְּקִידוּת, וְאֵינוֹ לְשׁוֹן מִנְיָן:

Appoint Aharon and his sons. The word connotes appointment, not counting.

ושמרו את כהנתם. קַבָּלַת דָּמִים וּזְרִיקָה וְהַקְטָרָה וַעֲבוֹדוֹת הַמְּסוּרוֹת לַכֹּהֲנִים:

And they shall guard their priesthood. Referring to the blood [of the sacrificial offerings], sprinkling [it on the altar], burning [the sacrifices], [and other] services entrusted to the kohanim.