Command the Israelites to bring you clear oil of pressed olives for the light so that the lamps may be kept burning

Exodus 27:1-21

Build an altar of acacia wood, three cubits high; it is to be square, five cubits long and five cubits wide. Make a horn at each of the four corners, so that the horns and the altar are of one piece, and overlay the altar with bronze. Make all its utensils of bronze—its pots to remove the ashes, and its shovels, sprinkling bowls, meat forks and firepans. 

Make a courtyard for the tabernacle. The south side shall be a hundred cubits long and is to have curtains of finely twisted linen, with twenty posts and twenty bronze bases and with silver hooks and bands on the posts. The north side shall also be a hundred cubits long and is to have curtains, with twenty posts and twenty bronze bases and with silver hooks and bands on the posts.

The west end of the courtyard shall be fifty cubits wide and have curtains, with ten posts and ten bases. On the east end, toward the sunrise, the courtyard shall also be fifty cubits wide. 

For the entrance to the courtyard, provide a curtain twenty cubits long, of blue, purple and scarlet yarn and finely twisted linen—the work of an embroiderer—with four posts and four bases.

Command the Israelites to bring you clear oil of pressed olives for the light so that the lamps may be kept burning. In the tent of meeting, outside the curtain that shields the ark of the covenant law, Aaron and his sons are to keep the lamps burning before the Lord from evening till morning. This is to be a lasting ordinance among the Israelites for the generations to come.

Why?

Keep the lamp burning, which means the Lord is with them always. 

This is the duty of Aaron, for only Aaron and his sons may enter the Tabernacle. Israelite has the duty to supply the clear oil of olives for the lights. 

Every Christian has the responsibility to serve the Lord in a different way and position.

How?

Serve the Lord with the capability that Lord gives me.