Describe symbolism in A Long and Happy Life by Reynolds Price

Rosacoke finds that she is pregnant and resolves to keep the news to herself, to keep Wesley from feeling a sense of responsibility, just as Mildred Sutton, who died during childbirth, never revealed the name of her child's father. She changes her mind, though, after visiting Mr. Isaac, an old man who is, mind and body, like a child. She tells Wesley about the baby, and he somewhat reluctantly agrees to marry her, but she refuses his offer until, during the annual Christmas pageant, Rosacoke (playing the Virgin Mary) comes to understand the baby that is representing the infant Jesus. She decides to marry for her child's sake, despite her own prospect for unhappiness.