In terms of the cultural purpose of myths...
In terms of cultural values, there is the story of Prometheus. He is said to have taken pity on humans and given them fire for light, cooking, and warmth. He was also responsible for tricking Zeus into accepting the poorer cut of meat offered by humans in sacrifice, so that humans could keep the better portion for themselves.
Because Zeus felt that Prometheus had gone beyond his place, and by sharing such a power with humans—and tricking Zeus— Prometheus is chained to a rock. His punishment is to have his liver eaten out each night by an eagle. Each morning it grows back. This punishment is perpetual, meant to continue for all time. (It is also said that Hercules eventually saves Prometheus, removing the chains that shackled him in place.)
An allegory shares a message or hidden meaning. In this case, Prometheus is found guilty of hubris. Zeus was careful to keep mankind subjugated: too much power might be a threat to the gods—if nothing else, humans might not look to the gods for help, or might not hold them in such high esteem, even fearing them less. Prometheus is seen as a protector of, and advocate for, mankind.
Prometheus [was] as a lowly challenger to Zeus's omniscience and omnipotence.
His desire comes from a sense of pity for humans sealed in a world of darkness and cold. He also wants them to have enough to eat. The message taken might be that "no good deed goes unpunished," a cynical statement at best. However, in that Prometheus is later released, it can be said that good deeds do not come without a risk, but ultimately simply doing the right thing rewards one.
Of course, this is my interpretation. However, this is something that is still relevant today in a modern society. Metaphorically speaking, bringing rights to African Americans during the Civil Rights Movement, Dr. Martin Luther King, Jr., was the Prometheus of his time: defying the powers that be to bring light and freedom—a better life—to those subjugated for so long.