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.
Ezekiel 12:2-3
2
Son of man, you dwell in the midst of the rebellious house, who have eyes to see, and don't see, who have ears to hear, and don't hear; for they are a rebellious house.
3
Therefore, you son of man, prepare your stuff for moving, and move by day in their sight; and you shall move from your place to another place in their sight: it may be they will consider, though they are a rebellious house.
