The priest in the temple used to prepare the candles in the Holy Temple. The Zohar reveals that the light comes down first on the head of the priest, that represents the upper three sefirot of Zeir Anpin, then he lights up all the candles that represent the sefirah of Malchut.
The process of preparing the candles was done twice a day, once in the morning and once in the afternoon, before sundown.
The candles in the Holy Temple were the vessels for oil, and the process of preparing them for the light was so high that no one was allowed to do that but the priests.
The Zohar quotes the Torah verses below to connect us to the energy that was revealed by the priests during their work in the Holy Temple.
“כַּשֶּׁמֶן הַטּוֹב, עַל-הָרֹאשׁ יֹרֵד, עַל-הַזָּקָן זְקַן-אַהֲרֹן: שֶׁיֹּרֵד, עַל-פִּי מִדּוֹתָיו.”
“It is like the precious oil upon the head, Coming down upon the beard, Aaron’s beard, Coming down upon the edge of his robes.”
“וְהַכֹּהֵן הַגָּדוֹל מֵאֶחָיו אֲשֶׁר-יוּצַק עַל-רֹאשׁוֹ שֶׁמֶן הַמִּשְׁחָה, וּמִלֵּא אֶת-יָדוֹ, לִלְבֹּשׁ, אֶת-הַבְּגָדִים–אֶת-רֹאשׁוֹ לֹא יִפְרָע, וּבְגָדָיו לֹא יִפְרֹם”
“’The priest who is the highest among his brothers, on whose head the anointing oil has been poured and who has been consecrated to wear the garments, shall not uncover his head nor tear his clothes”
“וּמִן-הַמִּקְדָּשׁ, לֹא יֵצֵא, וְלֹא יְחַלֵּל, אֵת מִקְדַּשׁ אֱלֹהָיו: כִּי נֵזֶר שֶׁמֶן מִשְׁחַת אֱלֹהָיו, עָלָיו–אֲנִי יְהוָה”
“He shall not go out of the sanctuary, lest he profane the sanctuary of his God, for the consecration of the anointing oil of his God is on him: I am YHVH.”
“שֶׁמֶן וּקְטֹרֶת, יְשַׂמַּח-לֵב”
“Oil and incense bring joy to the heart”
The priest was also preparing and burning the incense at the same time as he was preparing the candles. The oil was drawing the light and the incense deterring the negative side from coming closer to the Holy Temple.