The story of Prometheus's theft of fire is one of the most famous myths of the Ancient Greeks. Prometheus was one of the Titans of Greek mythology, said to have previously sided with the gods in their rebellion against Cronus, and he was the primary patron and protector of humanity (and often their creator). This special relationship is reflected in the story in question.
Ultimately, fire is one of the key symbols and enablers of human civilization: it can be used for cooking, warmth, or illumination (just to give a few examples), and in this respect, the mastery of fire still represents one of humanity's most important and far-reaching achievements. This association of Prometheus with fire and the image of Prometheus stealing fire from the gods and bringing it back to Earth to benefit man is a striking illustration of his close relationship with humanity and status as its protector.
However, it is also important to remember that Prometheus suffers excruciating agony for his rebellion. As the story continues, he is bound on a mountain and left at the mercy of an eagle that would gnaw each day at his liver. Being immortal, Prometheus cannot die, and so he is left to suffer.
In this sense, the story of Prometheus's theft of fire is also a story of intense personal sacrifice, one made out of love for humanity to ensure that they might thrive, even as he himself must pay a horrifying price.