That was another mystery: it sometimes seemed to him that venial sins—impatience, an unimportant lie, pride, a neglected opportunity—cut off from grace more completely than the worst sins of all. Then, in his innocence, he had felt no love for anyone: now in his corruption he had learnt
This quotation, from Chapter Three of Part II, is striking because of the way it sets up familiar contrasts only to rethink and rework them. 'Venial' sins, what we normally think of as very minor wrongs, are here suggested to be the very worst kinds of failing. Greene suggests that venial sins can pass unnoticed in people's day-to-day lives, and can add up—if unrepented for and unacknowledged—causing a kind of slow deadening of one's spirit. Greene then indicates that even though venial sins are worse, the people who commit them are actually more "innocent", presumably because they are unaware of how far they have really drifted from goodness. Interestingly it is actually in his "corruption" that the priest learns how to feel love. Greene's attitudes towards matters such as sin, innocence and grace are extremely important and also extremely complicated.