This is something I had never heard of before - it is a really beautiful custom from the Orthodox Church that has lasted from the earliest days of Christianity to today, 'brother - making', the making of two friends into brothers, or sisters, in the sight of God.
I won't use my own words to describe it. Theological historian Robin Darling Young speaks about this custom in this article from her own experience:
"This is a subject about which I have the good fortune to speak not merely as a scholar or an observer, but as a participant. Nine years ago I was joined in devout sisterhood to another woman, apparently in just such a ceremony as Boswell claims to elucidate in his book. The ceremony took place during a journey to some of the Syrian Christian communities of Turkey and the Middle East, and the other member of this same-sex union was my colleague Professor Susan Ashbrook Harvey of Brown University. During the course of our travels we paid a visit to St. Mark’s Monastery in Jerusalem, the residence of the Syrian Orthodox archbishop. There our host, Archbishop Dionysius Behnam Jajaweh, remarked that since we had survived the rigors of Syria and Eastern Turkey in amicable good humor, we two women must be good friends indeed. Would we like to be joined as sisters the next morning after the bishop’s Sunday liturgy in the Church of the Holy Sepulchre? Intrigued, we agreed, and on a Sunday in late June of 1985, we followed the bishop and a monk through the Old City to a side chapel in the Holy Sepulchre where, according to the Syrian Orthodox, lies the actual tomb of Jesus. After the liturgy, the bishop had us join our right hands together and he wrapped them in a portion of his garment. He pronounced a series of prayers over us, told us that we were united as sisters, and admonished us not to quarrel. Ours was a sisterhood stronger than blood, confirmed in the outpouring of the Holy Spirit, he said, and since it was a spiritual union, it would last beyond the grave.
Our friendship has indeed endured and flourished beyond the accidental association of two scholars sharing an interest in the Syriac-speaking Christianity of late antiquity. The blessing of the Syrian Orthodox Church was a precious instance of our participation in the life of an ancient and noble Christian tradition. Although neither of us took the trouble to investigate the subject, each privately assumed that the ritual of that summer was some Christian descendant of an adoption ceremony used by the early church to solemnify a state-that of friendship-which comes highly recommended in the Christian tradition (“Henceforth I call you not servants . . . but I have called you friends.” [John15:15]).
*Note - the existence this custom has been used by modern scholars to claim that the ancient Orthodox church had a form of same sex marriage - this is patently false, as the rest of the article shows.