9 Therefore also the Holy Spirit came as a dove, a simple and joyous creature, not bitter with gall, not cruel in its bite, not violent with the rending of its claws, loving human dwellings, knowing the association of one home; when they have young, bringing forth their young together; when they fly abroad, remaining in their flights by the side of one another, spending their life in mutual intercourse, acknowledging the concord of peace with the kiss of the beak, in all things fulfilling the law of unanimity.
This is the simplicity that ought to be known in the Church, this is the charity that ought to be attained, that so the love of the brotherhood may imitate the cloves, that their gentleness and meekness may be like the lambs and sheep. What does the fierceness of wolves do in the Christian breast? What the savageness of dogs, and the deadly venom of serpents, and the sanguinary cruelty of wild beasts? We are to be congratulated when such as these are separated from the Church, lest they should lay waste the doves and sheep of Christ with their cruel and envenomed contagion.
Bitterness cannot consist and be associated with sweetness, darkness with light, rain with clearness, battle with peace, barrenness with fertility, drought with springs, storm with tranquillity. Let none think that the good can depart from the Church. The wind does not carry away the wheat, nor does the hurricane uproot the tree that is based on a solid root. The light straws are tossed about by the tempest, the feeble trees are overthrown by the onset of the whirlwind. The Apostle John execrates and severely assails these, when he says, “They went forth from us, but they were not of us; for if they had been of us, surely they would have continued with us.”
Source: The Treatises of Cyprian (New Advent)