What is the significance of Reverend Whitfield?

Reverend Whitfield is the man with whom Addie has an affair during her marriage to Anse, and he is also the father of Jewel. Whitfield gets to narrate one chapter, and, during this section, we learn what a hypocrite his character is in terms of his religious beliefs and position.
As a reverend, we would first not expect Whitfield to be having an affair or fathering a child out of wedlock; however, it seems he and Addie had a brief romance during which she became pregnant with Jewel. In Addie's chapter, narrated from beyond the grave, she describes her affection for Jewel as being born out of her ability to make a choice to have the child with Whitfield; with Anse, sexual relations and childbearing become obligations. When Whitfield narrates his own chapter, we learn that he feels somewhat guilty to have committed adultery, but ultimately exposes himself as selfish and hypocritical. He has the misguided idea that he should go to Addie on her deathbed and confess their affair to Anse. This would only be to make him feel as though he is unburdened of the secret, but it would cause much confusion and trauma for the family on the eve of Addie's death. However, he doesn't end up doing this because Addie dies before he arrives. Whitfield sees this as a way of God forgiving him for what he did. He even refers to his situation as his own "Gesthemane," which shows his delusions of grandeur and self-centered nature (that is the garden where Jesus was praying when he was arrested by the Romans). He uses his faith to excuse his behavior, while presumably spouting guidelines of the faith, which he has not followed, to his congregation from his pulpit. Faulkner could be using Whitfield to expose the corruption of the Southern church and its clergy, as he similarly critiques class difference/poverty and the treatment of women.
Whitfield serves an important purpose in the plot as Jewel's father, explaining why Jewel is so separate from the rest of the family, but he also helps to illuminate some of Faulkner's themes.