Faith is one of only two things in mankind's consciousness that defies discussion. The other is one's marriage.

If you behave in a manner that poisons your relationship, don__ be surprised when it dies.

There is no such thing as escape after all, only an exchange of one set of difficulties for another. It wasn't Mark or the farm or marriage I was trying to shake loose from but my own imperfect self, and even if I kept moving, she would dog me all the way around the world, forever.

...[A] certain degree of un-understanding (not mis-, but un-) is the only possible sanctuary which one human being can offer to another in the midst of the devastating intimacy of a happy marriage.

Evil never goes unpunished, Monsieur. But the punishment is sometimes secret.

Nowadays, no one believes in evil. It is considered, at most, a mere negation of good. Evil, people say, is done by those who know no better - who are undeveloped - who are to be pitied rather than blamed. But, M. Poirot, evil is real! It is a fact! I believe in Evil as I believe in Good. It exists! It is powerful! It walks the earth!' He stopped. His breath was coming fast. He wiped his forehead with his handkerchief and looked suddenly apologetic. 'I'm sorry. I got carried away.