Ferenczi left some unfinished notes behind. One of them is "The three main principles" he wrote in 1932, and, in my opinion, contains the main ideas of group analysis:
The two opposing forces, the ego and the social.
They imply the dictum that one person alone is an abstraction.
The social part dissolves the person in the whole.
The ego protects the person from it happening.
Altruism, as genuine tendency, not as neurosis.