(With thanks to Zack in Rome):
St. Thomas Aquinas defined mercy as “the compassion in our hearts for another person’s misery, a compassion which drives us to do what we can to help him” (ST II-II.30.1).
In Love and Responsibility, the future pope wrote: “We love (the person) along with his virtues and vices, in a sense independently of the virtues and despite the vices. The greatness of this love is manifested the most when this person falls, when his weaknesses or even sins come to light. One who truly loves does not then refuse his love, but in a sense loves even more – he loves while being conscious of deficiencies and vices without, however, approving of them. For the person himself never loses his essential value.”