Cyprian of Carthage, On the Unity of the Church 9

That is why the Holy Spirit also descended in the form of a dove — a simple, happy creature, neither bitter with gall nor savage with bites nor violent with claw-tearing. It loves human dwellings and knows the fellowship of a single household; when it breeds, the parents raise their young together; when it travels, the flock stays together in flight; it lives its whole life in common companionship, seals the concord of peace with a kiss of the mouth, and fulfills the law of unanimity in everything. This is the simplicity that must be recognized in the Church, and this is the charity that must be obtained, so that the love of doves may imitate brotherly love, and gentleness and mildness may equal the character of lambs and sheep. What place do the savagery of wolves, the rage of dogs, the lethal poison of serpents, and the bloody cruelty of beasts have in a Christian heart? It is a thing to rejoice when such people are separated from the Church, lest they devour the doves and the sheep of Christ with their savage and poisonous contagion. Bitterness cannot cohere and be joined with sweetness, darkness with light, rain with serenity, conflict with peace, sterility with fertility, dryness with springs, or tempest with tranquility. No one should think that good people can leave the Church: the wind does not carry away wheat, nor does a storm overturn a tree founded on a solid root; empty chaff is tossed about by a tempest, and weak trees are uprooted by the onslaught of a whirlwind. The apostle John condemns and strikes these people, saying, "They went out from us, but they were not of us; for if they had been of us, they would certainly have remained with us" (1 John 2:19).