Friendship is unnecessary, like philosophy, like art... It has no survival value; rather it is one of those things that give value to survival.

This quote is saying that friendship is not necessary for survival, and in fact, surviving is what gives friendship its value. Friendships bring joy and meaning to our lives, but they are not essential in order to stay alive. Philosophies, and art, have similar qualities – they make life better, but they are not necessary for survival.