Positive commandment · Mitzvat Aseh #25 of 613
To prepare the candles of the Sanctuary
לַעֲרֹךְ נֵרוֹת בַּמִּקְדָּשׁ
The verse · Shemot 27:21
בְּאֹהֶל מוֹעֵד מִחוּץ לַפָּרֹכֶת אֲשֶׁר עַל־הָעֵדֻת יַעֲרֹךְ אֹתוֹ אַהֲרֹן וּבָנָיו מֵעֶרֶב עַד־בֹּקֶר לִפְנֵי ה׳ חֻקַּת עוֹלָם לְדֹרֹתָם מֵאֵת בְּנֵי יִשְׂרָאֵל
“In the Tent of Meeting outside the veil, which is before the Testimony, Aharon and his sons shall order it from evening to morning before the Lord: it shall be a statute for ever to their generations on behalf of the children of Yisra᾽el.”
The Rambam’s words
To prepare the candles of the Sanctuary, as [Exodus 27:21] states: "Aaron and his sons shall prepare it."
לַעֲרֹךְ נֵרוֹת בַּמִּקְדָּשׁ, שֶׁנֶּאֱמָר: "יַעֲרֹךְ אֹתוֹ אַהֲרֹן וּבָנָיו" (שמות כז, כא).
Why · Sefer HaChinuch #98
Arranging lights in the Temple
“It is from the roots of the commandment that G-d, may He be blessed, commanded us that there be a lit light in the Temple for the aggrandizement of the Temple, for [its] glory and splendor in the eyes of the seers.”
Who & when
“And [it] is practiced at the time of the Temple by priests.”
Where in the Mishneh Torah
Hilchot Daily Offerings and Additional Offerings הלכות תמידים ומוספין