What is the theme in The Cider House Rules by John Irving?

The primary theme throughout the entire novel is that of good versus evil. Biblical symbolism runs throughout the book, exemplified by the nurses' nickname for Dr. Larch, "St. Larch." Homer has an inner struggle with good versus evil when it comes to Dr. Larch performing abortions. Homer doesn't realize that the fetus is a living being until he reads it in Gray's Anatomy, and this is when Homer decides that abortion is wrong and vows never to perform one.