Oil
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.
Arcana Coelestia # 7715
7715. 'Three days' means a state made complete. This is clear from the meaning of 'three days' as a state made complete, dealt with in 2788, 4495. By a state made complete one should understand an entire state from beginning to end; for every state has its beginning, stages of development, and highest point, this period being what one should understand by a complete period and what is meant by 'three days'.