Anonymous asked - "What do you consider more important regarding the social context of the book - Selfishness or Sacrifice?"
The plague years were a time of extreme social stress. Whole towns could die overnight and no one really knew why. In a social environment of fear and hysteria people will react differently depending on their immediate environment.
For example, Katherine had a different social context than Father Simon. She was the leader of her immediate social group and lived in harmony with a large number of servants and tenants. It was a supportive community and so she more easily felt a sense of moral responsibility toward her people and would make the sacrifices necessary to keep thenm safe.
Father Simon on the other hand, lived in virtual isolation with a few servants who feared and hated him. Albeit of his own making, his social context was one of loneliness, hostility and mistrust. Feeling excluded from general society it was much easier for him to react selfishly and vindictively.
I don't think one response is more important than the other. Both are significant and act like a mirror to reflect the realities of human nature within immediate social context. I personally value sacrifice over selfishness so sacrifice played a larger role in the book.