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 4:17-21
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The book of the prophet Isaiah was handed to him. He opened the book, and found the place where it was written,
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"The Spirit of the Lord is on me, because he has anointed me to preach good news to the poor. He has sent me to heal the brokenhearted, to proclaim release to the captives, recovering of sight to the blind, to deliver those who are crushed,
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and to proclaim the acceptable year of the Lord."
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He closed the book, gave it back to the attendant, and sat down. The eyes of all in the synagogue were fastened on him.
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He began to tell them, "Today, this Scripture has been fulfilled in your hearing."
