According to Moses, God wanted the people of Israel to bring clean olive oil to keep lamps burning all the time. This was important so that there would always be light in a special place for God.
Leviticus 24:2: Command the children of Israel, that they bring unto thee pure oil olive beaten for the light, to cause the lamps to burn continually. [to cause: Heb. to cause to ascend]
This verse reinforces the same command as Leviticus 24:2 rather than contradicts, showing consistency in instruction.
Exodus 27:20: And thou shalt command the children of Israel, that they bring thee pure oil olive beaten for the light, to cause the lamp to burn always. [to burn: Heb. to ascend up]