The king as a religious metaphor
The king is aloof, demanding, and self-serving, but by the end of the novel, the protagonist truly wishes he had done anything to stay on the king's good side. Although the king is seemingly capricious, being on the king's side means that the king's blessing remains. By the end of the story, the character is left in the same place as the Prodigal Son—rock bottom. He dreams of restoration. This also parallel's his relationship to existence and to his own life. Robert is the kind of person who is willing to hurt other people, so his experience of the justice of the universe makes it easy for him to become bitter. By the end, he wishes he had done it another way.
Celia as the femme fatale
To Robert, Celia isn't really a wife. Romance is a type of friendship, so marriage implies real emotional intimacy. Celia doesn't represent life or love, she represents selection, competition, and jealous anger. Robert is perplexed by Celia's rejection, making her into the anima, or the femme fatale. She sets the standard for Robert's self-esteem issues, and when he goes to try to love himself, it will be her rejection that makes him think twice.
The Quaker medic
Robert is a failed doctor, but he has a friend named Pearce who finished his degree and works at a mental health hospital. Notice that Robert points at Pearce's religion as a core part of his work. That means that Pearce simultaneously represents bodily, mental, and spiritual health. He is like a shaman in the story who does what he can, but knows that every person has to make their own ethical choices. He loves Robert, but he can't make Robert's problems just go away; Robert has to set those goals and attain them on his own.
The motif of plague and sickness
The inclusion of sickness and death is obvious in the story. The people of London are sick, smitten with a plague that is killing off the town slowly. But that is a metaphor for some other kind of sickness, a sickness that perhaps Pearce and the Quakers might have a remedy for in their old-timey ways. This is a spiritual illness, and we can see that in the end, when Robert picks selfish victimhood instead of sacrificing for others, he makes himself sick. So the sickness is a metaphor basically arguing that the universe punishes hateful people.
The motif of loneliness
The characters in this novel are driven by human intimacy. They are desperate for human love, affection, and adoration. The novel's dysfunction is originally introduced by the king who cannot find satisfaction in any of his relationships, so he tries with Celia. But Robert sees that Celia is worth true love, not just the king's cheap amusement. No one in this love triangle is happy, especially not Robert who has sold his chances at love for money. Then Robert afflicts Katherine with rejection and loneliness, unable to find in her what he found in Celia. But that is because Robert is not humble enough to really try with Katherine. He's just using her, and when she gets pregnant, he doesn't care about her or the child. His loneliness is perpetuated by his willingness to use and hurt people.
