Draper describes the flame in such a way that it tells us as much about Gerald's feelings as it does about the flame.
She doesn't just say it was orange and hot, or that it was a healthy flame because there was lots of fuel in the lighter, or that it was the size of a fingernail.
Instead she says the flame dances, smiles, and bows for him; it changes colours, it flickers magically, and so on.
What she is doing is describing the flame from Gerald's point of view. This description helps us see the flame how he sees it—and knowing that he sees the flame that way helps us imagine how he feels.
For example, we can imagine that if we saw a magical dancing flame, we might be so entranced that we don't notice the curtains have caught fire while we're playing with it.