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.
Luke 11:33-36
33
"No one, when he has lit a lamp, puts it in a cellar or under a basket, but on a stand, that those who come in may see the light.
34
The lamp of the body is the eye. Therefore when your eye is good, your whole body is also full of light; but when it is evil, your body also is full of darkness.
35
Therefore see whether the light that is in you isn't darkness.
36
If therefore your whole body is full of light, having no part dark, it will be wholly full of light, as when the lamp with its bright shining gives you light."
