they do not know who’s the Saint and who’s the Sinner.

The Sinner obviously think he’s the Saint and the Saint is the Sinner, while the true Saint thinks the opposite because he is a Saint.

Moral of the story: Do not make judgements based on superficial attributes and incomplete information, you never know who’s right. Maybe, you shouldn’t make judgements at all, because there is no right or wrong in many matters.