Emor - The Power of Seven

Command the children of Israel, and they shall take to you pure olive oil, crushed for lighting, to kindle the lamps continually.

צַו אֶת בְּנֵי יִשְׂרָאֵל וְיִקְחוּ אֵלֶיךָ שֶׁמֶן זַיִת זָךְ כָּתִית לַמָּאוֹר לְהַעֲלֹת נֵר תָּמִיד
Vayikra 24:1

The Orach HaChaim asks, what this passage is doing here? What is the purpose of the oil and lighting the menorah, as well as the regiment of showbread appearing at this place? Moreover, these nearly exact words already appeared earlier on in the Torah (Shmot 27:20), so why repeat here?