Community is an important part of individual success
In the novel, Ned is forced to collaborate with his father, a difficult task emotionally. But when he does, he finds out that the bench is deeper than he thought, meaning that there are more people who can help him. Their assistance, along with his valor, is what leads Ned to victory. The thematic reading of this would be that without investing in others and being vulnerable are essential parts of successful living.
Historically, all humans are part of the same story
By closely linking feudal France with modern times, the author is showing that Ned's story is continuous with the history of the earth, a theme also responsible for the inclusion of cathedrals and ruins.
People aren't objects to be obtained
This theme is included in the novel in an interesting way. By including a spiritual possession, the question is raised as to people's rights to their person. It feels morally wrong for someone to possess a vessel, which is the moralistic aspect of the imagery. The author is touching on an insidious habit that has existed in the West to dehumanize women and use them as objects, like slavery. And indeed in the climax, it's because of altruism and empathy that Ned survives and saves Melanie, and the suitors failed because they were treating love as an object to be obtained.
