Fire is an important symbol in Frankenstein for many reasons.
1. Dr Frankenstein is compared to a 'modern Prometheus': Prometheus, in Greek mythology, gave fire (which symbolized knowledge) to humans and then suffered an eternal punishment for that. Frankenstein is trying to bring his own gift of knowledge (life) to humanity but his life is also ruined through this process.
2. Fire also is something that has two sides, each that can help or hurt. Building a fire can create warmth and light, but too much of it can cause death and destruction. This is also shown through Frankenstein's creation of the monster. Think of the saying "playing with fire". (In a more specific instance, when the monster realizes that fire can destroy he uses it as a weapon (burning the villager's cottage) )
3. Fire also represents passion and desire. Both Frankenstein and the monster possess this fire--Frankenstein for knowledge and creation, the monster for acceptance. This fuels both of their efforts through the novel.
