This phrase is used to suggest that it is important to separate an individual from their actions. It means that even though someone might do something wrong or bad, it is important to remember that it is not the same as the person themselves. The phrase “hate the sin” is a reminder to find fault with someone’s actions, not the person as a whole. On the other hand, the phrase “love the sinner” is a reminder to still have compassion for the individual—despite any mistakes they might have made.