In Katherine Anne Porter's short story, "The Grave," I believe the main theme would reflect the story's title.
The story's plot revolves around the grave of the Miranda and Paul's grandfather (and other relatives), that has been moved, and the property where it rested has been sold.
Miranda, nine, and her brother Paul, twelve, find the open graves while out hunting, and with innocence, jump in to explore. Each finds something of interest: a silver dove and a gold ring. They trade their "treasures," and continue hunting .
When Miranda places the gold ring on her finger and looks at the boyish clothes she wears, she has a sudden urge to dress more like a girl, wearing a dress. In that moment she begins to become aware of her femininity.
Meanwhile, Paul has shot a rabbit. After he skins it, they realize it was pregnant. Opening the flesh that has held the unborn animals, they are both saddened and awed, and decide to tell no one. However, as Miranda looks at the lovely dead creatures, she also becomes aware of the cycle of life--of birth, and coming close on the heels of the grave: death, not only of those in the cemetery, but also of the mother rabbit and her unborn offspring. There is a poignant moment of awakening for young Miranda. They replace the bunnies in the mother's womb, making it their grave: they wrap the carcasses in the animal's skin, hide it in the bushes and leave.
Many years later, Miranda is on the street in a foreign city. A man is selling dyed candy, molded in the shapes of small animals. There is meat being sold in the marketplace, as well as wilting flowers. All of these things come together to take Miranda back to the day in the woods when she was nine years old--where she had crossed the threshold from innocence into knowledge of the world, where her own femininity and the inevitability of birth to death had been realized. The harshness of that enlightening moment is softened in her mind with a glimpse of a memory of her brother on that day. He stands in brilliant sunshine, wearing a serious smile while studying the silver dove in his palm.
The grave literally refers to the resting place of Miranda's dead relatives. It also brings to mind the womb where the bunnies are buried in the underbrush.
It can symbolize, as well, the death of Miranda's innocence. However, the vision of the brilliant sunshine and the dove her brother carries in her flashback remind her of images of rebirth associated with the sun and dove; in this way the memory does not have to be associated with the darkness that so often accompanies the perception of a grave, but can give her hope in the rebirth that can follow that perception. This is the main theme. In other words, when she left her innocence behind her, it also opened a world of possibilities to her that had been hidden from her prior to that moment. This ending provides the reader with a sense of hope at the story's end, rather than a feeling of loss.