Graham Greene is revisiting his old topic of the sins of those who love being much better than the sins of those who don't love, but it is fascinating and really well done when the two people contrasted are lovers, rather than dreary as in The Power and the Glory. And now it is moving into an even better topic: the discovery that one is loved when one could hardly deserve it less.
The book visits a topic I've been mulling over. Are the easiest people to love those who find it easy to be loved? I read somewhere that when God begs us to be as little children what He is referring to is how they just assume that people will love them, so they accept His love. But for adults there is amour propre and self-consciousness and woundedness and all the rest.