Samuel anointed David with oil to designate him as the crown-prince, the successor of Saul. But why oil?

Oil is food. It is one of the main ingredients of bread in Scripture, and a food in its own right. With grapes and grain, oil is one of the main products of the promised land. Oil is the fat of the land. By his anointing, David is designated as the one who will lead Israel from Philistine threat to a land flowing with milk and honey, dripping with wine and oil.

Oil consecrates. When Moses built the tabernacle, he sprinkled oil on it and all its furnishings to consecrate it as holy space. By his anointing, David is consecrated as a holy man.

Oil is cosmetic. It makes the face to shine with a glorious sheen that replicates the radiant glory of the face of Yahweh. By his anointing, David is glorified.

Oil is fuel. Oil was burned in the lampstand in the holy place of the tabernacle, and in the multiple lampstands of the temple. By his anointing, David is filled with oil to become a lamp in Israel, a lamp that never goes out during the long years of Israel’s apostasy.

But not only David: John says that you too are anointed. You have been consecrated; be holy. You are lights; let your light shine. You have been given a share in the promised land; so, open your mouth and the Lord will fill it.