Aelred of Rievaulx

What statement about friendship can be more sublime, more

true, more valuable than this: it has been proved that friendship must begin in Christ, continue with Christ, and be perfected by Christ. . . .

A friend is called the guardian of love, or, as some prefer, the guardian of the soul itself. Why? Because it is proper for my friend to be the guardian of mutual love or of my very soul, that he may in loyal silence protect all the secrets of my spirit and may bear and endure according to his ability anything wicked he sees in my soul. For the friend will rejoice with my soul rejoicing, grieve with it grieving, and feel that everything that belongs to a friend belongs to himself.

Friendship is that virtue, therefore, through which by a covenant of sweetest love our very spirits are united, and from many are made one. Hence, even the philosophers of this world placed friendship not among the accidents of mortal life but among the virtues that are eternal. Solomon seems to agree with them in this verse from Proverbs: “a friend loves always.” So he obviously declares that friendship is eternal if it is true, but if it ceases to exist, then although it seemed to exist, it was not true friendship. . . . 

Source: Aelred of Rievaulx, Spiritual Friendship, trans. Lawrence C Braceland, SJ ­(Liturgical Press, 2010), Book 1, 10, 20–21.

‍