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.

177. THE GARMENTS WITH WHICH ANGELS APPEAR CLOTHED.

Since angels are men, and live among themselves as men do on the earth, they have garments and dwellings and other such things, with the difference, however, that as they are in a more perfect state all things with them are in greater perfection. For as angelic wisdom surpasses human wisdom to such a degree as to be called ineffable, so is it with all things that are perceived and seen by angels, inasmuch as all things perceived and seen by them correspond to their wisdom (see above, 173).