What is a charitable heart? It is a heart which is burning...

What is a charitable heart? It is a heart which is burning with love for the whole creation, for men, for the birds, for the beasts … for all creatures. He who has such a heart cannot see or call to mind a creature without his eyes being filled with tears by reason of the immense compassion which seizes his heart; a heart which is softened and can no longer bear to see or learn from others of any suffering, even the smallest pain being inflicted upon a creature. That is why such a man never ceases to pray for the animals … [He is] … moved by the infinite pity which reigns in the hearts of those who are becoming united with God.

Isaac of Nineveh

Mystic Treatises, cited in Vladimir Lossky, The Mystical Theology of the Eastern Church (1976), p. 111; also cited and discussed in A. M. Allchin, The World is a Wedding (1978), p. 85. Quoted in Andrew Linzey, Animal Theology (1994), p. 56.