Olive oil was precious in the ancient world — food, fuel, medicine, and the substance of anointing. Kings, priests, and prophets were anointed with oil to set them apart for God's service, the oil symbolising the Holy Spirit poured out on them. The very word Messiah (and Christ) means the Anointed One. Oil also meant gladness and healing — thou anointest my head with oil; my cup runneth over.
The good Samaritan poured oil on the wounded man; the sick were anointed with oil and prayer; and the wise virgins kept oil for their lamps. Behind all these uses lies the picture of the Spirit — the anointing that heals, gladdens, equips, and burns steady through the long night of waiting. To be anointed is to be marked out, filled, and set apart for God.
Oil in Scripture
Thou preparest a table before me in the presence of mine enemies: thou anointest my head with oil; my cup runneth over.