John Cassian (c. 360–435 AD) was a monk, theologian and mystic based in Marseille, France. His spirituality and writings had far-ranging influence, not least on Benedict of Nursia and Gregory the Great.
Cassian was deeply attracted to the desert monasticism of the Near East. He and a monastic friend Germanus toured Palestine and Egypt, visiting monasteries and recording impressions and conversations. This formed the basis of Cassian’s work, Conferences, dated to around 415. It is available in PDF format here.
In Conference 16: On Friendship, he and his friend record a conversation with Abbot Joseph at a monastery in Egypt. The abbot touches on human relationships:
Nothing is more damaging [to true friendship] than anger and vexation. Our enemy, the devil, sows the seeds of discord even between spiritual persons, on the ground of some difference of thinking. Therefore it is of no use to have removed the first ground of discord, which arises from the outward things of this world, unless we also cut off the second, which arises from wrong feelings. In everything we must gain humble thoughts and harmonious wills.
He goes on to look at the subtle differences between love and affection. Joseph maintains that “agapé” love (the New Testament word for Christ-like, self-sacrificing love) can be shown by Christians to anyone, on the basis of “doing good to all people, especially those who are of the household of faith” (Galatians 6:10). Genuine heart-affection, however, he sees as shown only to a few: those who are united to us by kindred dispositions or by a tie of goodness. There are levels to this, he points out, and they are variable: not all parents love their children to the same degree.
The remainder of Conference 16 is concerned with a more specifically monastic danger: of conforming and going through the motions of true brotherly affection, when the heart has lost the desire for it. This is the danger for any church, community or missional movement today, since drift is endemic to human nature.
All this made an impression on Cassian and Germanus, who conclude: Thus the blessed Joseph discoursed on spiritual friendship, and fired us with a more ardent desire to preserve the love of our fellowship as a lasting one.