What is the theme in Mercy by Jodi Picoult?

Love is the major theme of this story. Jamie loves Maggie so deeply that he kills her in order to take away her pain. Jamie loves Maggie more than she loved him and confesses to Allie that he believes that all marriages are not fifty-fifty, but sixty-forty or seventy-thirty. Jamie thinks his marriage was normal, that it is normal for one partner to love the other more. However, as Jamie grieves for his wife he begins to see his marriage the way others saw it. Maggie loved Jamie, he does not doubt that, but she never thought about what might happen to him if he helped her to die.