What is the theme in The Secret Garden by Frances Hodgson Burnett?

One of the overarching themes of The Secret Garden is the concept of rebirth. In a manner of speaking, Archibald Craven died along with his wife when she fell to her death in the garden 10 years earlier. He retreated into his grief and refused to interact with his son because Colin reminded him of his mother. He also had the garden his wife had loved locked away. He buried the key much as we bury the dead in our society. Mary also experiences death after her parents succumb to a cholera epidemic. Her life changes forever when she is sent to live with her uncle. Although he is alive, Colin senses death over his shoulder at all times and is haunted by the portrait of his dead mother, keeping it covered at all times.