Shannon ends up being a vibrant voice of reason throughout the book, as his actions begin to bring the scrutiny of his religious community. For instance, he ends up literally excommunicated from his church for having sex with a Sunday school teacher, which makes sense in the morality of the South, but it doesn't make sense whatsoever to Shannon. He says God is a "senile delinquent," but then again, there are echoes of delinquency in his own mistreatment of the girl.
Another important thing to remember about Shannon's indiscretion is that the girl wants to marry him, even though he literally attacks her, hitting her head. Her willingness to attach herself to him is a dual symbol to the reader. One, it means that she is unlikely to take care of herself properly, because she is excited by the sex, but her religious beliefs push her toward commitment when obviously, Shannon is not the one.
Secondly, her willingness to attach herself to a violent person might be a suggestion that her culture is setting her up to accept abuse. In the denouement, the discussion about eating or not eating the iguana invokes the question of sacrilege and innocence again, but the symbol becomes further confused by Nonno's spontaneous eruption into perfect poetry, and then his death. The idea of experience and innocence ends up being the closing chord to this novel, because Nonno's death is a symbol of experience.
