“You shall command the children of Israel that they should take for you clear olive oil, crushed for illumination, to keep the lamp burning continually.” (Exodus 27:20)
Rabbi Avin HaLevi said: When someone wants to make a window, he makes it wide from within and narrow from without. Why? So that it should draw in the light. Yet, the windows of the Holy Temple were wide from without and narrow within. Why? So that the light would leave the Temple and illuminate the world. (Midrash Tanchuma)