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.
Micah 7:1-2
1
Misery is mine! Indeed, I am like one who gathers the summer fruits, as gleanings of the vineyard: There is no cluster of grapes to eat. My soul desires to eat the early fig.
2
The godly man has perished out of the earth, and there is no one upright among men. They all lie in wait for blood; every man hunts his brother with a net.
