Cyprian on the church.
The Church also is one, which is spread abroad far and wide into a multitude by an increase of fruitfulness. As there are many rays of the sun, but one light; and many branches of a tree, but one strength based in its tenacious root; and since from one spring flow many streams, although the multiplicity seems diffused in the liberality of an overflowing abundance, yet the unity is still preserved in the source.
Separate a ray of the sun from its body of light, its unity does not allow a division of light; break a branch from a tree,-when broken, it will not be able to bud; cut off the stream from its fountain, and that which is cut off dries up.
Thus also the Church, shone over with the light of the Lord, sheds forth her rays over the whole world, yet it is one light which is everywhere diffused, nor is the unity of the body separated. Her fruitful abundance spreads her branches over the whole world. She broadly expands her rivers, liberally flowing, yet her head is one, her source one; and she is one mother, plentiful in the results of fruitfulness: from her womb we are born, by her milk we are nourished, by her spirit we are animated.
On the Unity of the Church, I,5.