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.

3220. When angels are engaged in discussion about matters of intelligence and wisdom, and about perceptions and cognitions, their discussion at the same time passes on from them into corresponding communities of spirits. Their discussion falls into representations involving such things as occur in the vegetable kingdom - into representations of paradise-like gardens, vineyards, woodlands, meadows with flowers, and into many other lovely things, which are quite beyond human imagination. This explains why things that constitute wisdom and intelligence are described in the Word as gardens, vineyards, woodlands, and meadows, and why such things are meant whenever these places are mentioned.