From St. Isaac of Nineveh,
An elder was once asked, “What is a compassionate heart?” He replied:
“It is a heart on fire for the whole of creation, for humanity, for the birds, for the animals, for all that exists. At the recollection and at the sight of them such a person’s eyes overflow with tears owing to the vehemence of the compassion which grips his heart. As a result of his deep mercy his heart shrinks and cannot bear to hear or look on any injury or the slightest suffering of anything in creation.
That is why he constantly offers up prayer full of tears, even for the irrational animals and for the enemies of truth, even for those who harm him, so that they may be protected and find mercy.
He even prays for the reptiles as a result of the great compassion which is poured out beyond measure --- after the likeness of God --- in his heart.” .