Symbolism, Imagery, Allegory
You probably noticed that there's a lot of fire in this book. Some of it is really hard to miss, like the first fire the Time Traveller starts, which gets out of control and burns down the forest (9.2). (Smokey the Bear is not going to be happy.) There are several smaller fires that are important in the story, too, like when the Time Traveller uses his matches to escape the Morlocks (6.11). These are examples of fire playing a really central role in the plot.
There are other fires that might be easier to miss. For instance, the Time Traveller uses his matches to amuse the Eloi and distract Weena from an upsetting topic (5.35, 5.41). We even find fire in 1890s London. When the Time Traveller demonstrates his model time machine, for instance, he places it in front of the fireplace so that everyone in the room can see it clearly (1.53). There's also the time when the Time Traveller lights his pipe using a spill (a long, thin piece of wood or rolled paper) – bad for his health, but good for proving how important fire is in the novel (1.62).
There are also times when the absence of fire is important: for instance, when the Time Traveller and Weena lie down to rest in the forest by a bonfire and wake up to discover that it has gone out and the Morlocks are attacking (9.9).
So why does fire play such an important role in the novel? For one thing, as the Time Traveller observes: "what a rare thing flame must be in the absence of man" (9.3). In other words, it's people who make fire. Our use of tools is one thing that sets us apart from other animals, and fire is one of our most important (and maybe oldest) tools.
However, that doesn't mean that fire is always our friend. Fire can be useful (for fighting off the Morlocks and seeing things at night), but it can also be misused. And fire can become dangerous, as we see when it burns down the forest and probably kills Weena.
So perhaps fire symbolizes technology in the novel. Like any technology, fire can be used or misused, and it can have unintended consequences. Technology makes our lives better, but – if you believe the premise of the novel – it can make humans lazy and ultimate lead to their demise.