Fire consumes a tree, and in so doing transforms it into its own image. The tree becomes fire because the fire eats it.
This is a law: everything, every being, becomes identical to that which consumes it. This is also true of ourselves.
If we offer our whole being to the fire of divine love, to be possessed and devoured by it, it will make us into its own image. We possess within us sufficient matter to feed the divine fire throughout eternity.
This is why we should meditate on fire; by trying to understand how it works on the tree to transform it into light and warmth, we too shall become trees of light.