This unity [among the three Persons of the Trinity] is nothing other than pure being-for-one-another. If there were a definition of God, then one would have to put it in the form: unity as being-for-one-another…. One cannot understand the Father except in his giving of himself in the begetting of his begotten Son, nor can one understand the Son except in his being for the Father. The self-giving of both to each other’s further a “being-for-one-another” which in the writings of the New Covenant is clearly distinguished as “Holy Spirit” both from the Father and from the Son; it is personified “being-for-one-another" itself and the total self-giving of God to men.
HANS URS VON BALTHASAR Elucidations, 92-93
[Christ’s “forness”] has no other goal than to free men from the prison of “for self” and to introduce them to the shape of divine freedom.
HANS URS VON BALTHASAR You Have Words of Eternal Life, 89