Gregory the Dialogist

But this sacrifice of good will is never fully paid unless desire for this world is perfectly abandoned. For whatever we covet in it, we without doubt envy our neighbors. For it seems that what another obtains is lacking to us. And because envy always conflicts with good will, as soon as the former seizes the mind, the latter departs. Therefore the holy preachers, that they might perfectly love their neighbors, strove to love nothing in this age, never to desire anything, to possess nothing even without desire. Looking upon them well, Isaiah says: "Who are these that fly as clouds, and as doves to their windows?" For he saw them despise earthly things, draw near to heavenly things in mind, rain down words, flash forth miracles. And those whom holy preaching and sublime life had lifted up from earthly contagions, he calls both flying and clouds. Moreover our windows are our eyes, because through them the soul looks upon what it desires outwardly. But the dove is a simple animal, and free from the malice of gall. Therefore they are as doves to their windows who covet nothing in this world, who look upon all things simply, and are not drawn by the zeal of rapacity in what they see. But on the contrary, the kite and not the dove is at its windows, who pants with desire for plunder at what it considers with its eyes.