Without even attempting to summarise a book of such great depth or to convey fully the context of the mention of adopted brotherhood, I shall translate what Father Florensky has to say on this particular subject. This excerpt begins two paragraphs before the discussion of adopted brotherhood, so that the reader may have some idea of its context.
Friendship bestows the greatest joy, but it also demands the greatest effort.
Every day, every hour, every minute, as the Ego with sorrow loses its life for the sake of the Friend, it joyfully finds that life restored. Just as agape towards a person brings forth philia for that person, so also in friendship mighty agape is embodied in philia as in a vital medium. To understand this laying down one's life for one's friends as meaning to die for them would be an oversimplification. Nevertheless, the essence of friendship really lies in laying down one's life for the sake of a friend. This means the sacrifice of one's whole organisational structure, one's freedom, one's calling.