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.

9601. 'And the breadth four cubits' means the marriage of truth to good. This is clear from the meaning of 'the breadth' as truth, dealt with in 1613, 3433, 3434, 4482, 9487; and from the meaning of 'four' as a joining together, dealt with in 1686, 8877, and so a marriage since truth and good joined together is called the heavenly marriage, 2173, 2618, 2728, 2729, 2803. 'Four' means a joining together or a marriage because this number is the product of two multiplied by itself, and 'two' means a joining together, 5194, 8423, multiple numbers being similar in meaning to the simple ones that are their factors, as stated immediately above in 9600. All numbers in the Word mean spiritual realities, see the places referred to in 9488.