It is what allows us to move from one to the other, from the affective to the ethical order, from what we feel to what we want, from what we are to what we should be.
Most virtues only aim at humanity, this is their greatness and also their limit. Compassion, on the other hand, universally sympathises with everything that one can suffer, which makes it the most universal of virtues.
A pearl of wisdom based on it, or sustained by it, would be the most universal and the most necessary, without which all human wisdom would be too human, or rather, too little.
It is the singular virtue that opens us not only to all humanity but to all living beings. To be human also with animals constitutes the clearest superiority that humanity can boast.