Today, the Middle East is thought of as a key source of petroleum, but in Bible times, most of the oil mentioned refers to olive oil. Other oils, such as castor oil and sesame oil, were used much more rarely.
Olive oil, which burns very brightly and has very little odor, was used for illumination. It was also used in ointments and so had an association with healing. Mary Baker Eddy brought the association of healing and oil to a spiritual level in her definition of oil, which Science and Health with Key to the Scriptures explains as: "Consecration; charity; gentleness; prayer; heavenly inspiration" (p. 592).
