"And what is a merciful heart? It is the heart's burning for the sake of the entire creation, for men, for birds, for animals, for demons, and for every created thing; and by the recollection and sight of them the eyes of a merciful man pour forth abundant tears. From the strong and vehement mercy that grips his heart and from his great compassion, his heart is humbled and he cannot bear to hear of or to see any injury or the slight suffering of anything in creation. For this reason he offers up tearful prayer continually even for irrational beasts, for the enemies of truth, for those who harm him, that they be protected and receive mercy. And in like manner he even prays for the lowest as a result of the great compassion which -- after the likeness of God -- is poured out beyond measure within his heart."
- Saint Isaac the Syrian