Charles Ellicott Commentary Exodus 27:20

"And thou shalt command the children of Israel, that they bring unto thee pure olive oil beaten for the light, to cause a lamp to burn continually." — Exodus 27:20 (ASV)

THE OIL FOR THE LAMP.

You shall command the children of Israel that they bring you pure olive oil. —This instruction had already been given (Exodus 25:2; Exodus 25:6), only not with such particularity. “Oil” had been required, but not “pure olive oil beaten.” By this is meant the best possible olive oil—that which was obtained by “beating,” or pounding in a mortar, which was free from various impurities found in the oil crushed out in the usual way in a mill.

To cause the lamp to burn always —i.e., every night without intermission. Josephus says that three lights were kept burning both night and day (Ant. Jud., iii. 7, § 7); but there is nothing in Scripture to confirm this. The tabernacle would have received sufficient light during the daytime through the entrance curtain, which was of linen (Exodus 26:36), not to mention that the curtain could also be looped up when necessary. The lighting of the lamps every evening is distinctly asserted in Exodus 30:8; their extinction in the morning appears from 1 Samuel 3:3.