Midrash su Salmi 30:10

And thou shalt command the children of Israel, that they bring unto thee pure olive oil beaten for the light (Exod. 27:20). The Israelites declared: Master of the Universe, it is stated: By Thy light shall we see light, yet You commanded us to kindle lights before You. R. Isaac related an anecdote about a house filled with lighted torches. The master of the house told his servant: “Light some lamps for us in the courtyard.” “But the house is fully lighted,” he replied, “why do you bid me to light lamps in the courtyard?” He answered: “Do it so that the servants will have light.”