Oil -- typically olive oil -- symbolizes the good that comes from celestial love. Celestial love is love of the Lord, the highest and purest love we can have. The good of celestial love is the desire to be good springing from celestial love: Wanting to do the Lord's will because you love Him. That's not a state many reach, even in heaven, but it's a beautiful goal. This representation makes sense based on the idea that the sun -- the source of all natural light and heat, and thus all natural life -- represents the Lord, the source of all spiritual light, heat and life. Burning oil was the most pure fire available in Biblical times, thus the closest representation of the sun people could create.

3222. In addition to this, loves and the affections belonging to them are represented by means of flames, which are indescribably varied. Truths however are represented by means of lights and by means of countless modifications of light. From this it may be seen how it comes about that flames in the Word mean goods that are the goods of love, and lights truths that are the truths of faith.