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.

128. The worldly and bodily-minded man says at heart, Unless I am taught about faith and about things that belong to faith by means of sensory evidence so that I see for myself, that is, by facts so that I understand for myself, I am not going to believe. And he confirms himself in this attitude from the consideration that natural phenomena cannot be at variance with spiritual. Consequently it is from sensory evidence that he wishes to learn about heavenly and Divine matters. But this is no more possible than for a camel to pass through the eye of a needle. The more he wants by this method to become wise, the more he blinds himself, until in the end he believes nothing, not even in the existence of anything spiritual or in eternal life. This arises out of the basic assumption he makes. This is eating from the tree of the knowledge of good and evil. And the more he eats of it, the more dead does he become. But the person who wishes to be made wise not from the world but from the Lord says at heart that he must believe the Lord, that is, those things the Lord has spoken in the Word, because they are truths. This is the basic assumption of his thinking. He confirms himself by means of rational, factual, sensory, and natural evidence. And things that are not confirmatory he sets aside.