Earlier in the book it talked about there not being a good guy. Everyone has their flaws because nobody is perfect. We believe in things all the time. What we “know” we also believe. When someone throws that stuff away then you giving up on things you “know”/believe. The parson is a religious man and he threw away so much of what makes us human. People argue over stuff they “know” or believe because they believe it is true. Conor believes his mom can be healed, but others seem to believe/”know” that she will die. Conor doesn’t want her to die, and nobody else does.