‘I-ThouWe’ relationship has itself absolute, divine value: in the triune being of love. It is not possible to divorce the Christian love of neighbor from this theological presupposition, but one sees what Christianity is only by participating in the divine movement from the ‘vertical’ to the ‘horizontal’. This is shown once again in the synthesis that Jesus effects—as the profoundest self-expression of his existence and his mission—between the chief commandment of the love of God and the commandment of the love of neighbor which is ‘equal to it’ (Mt 22.39). Although both of its presuppositions already existed, this synthesis is absolutely creative; it is identical with the unique Christological synthesis itself, as this is given expression by Chalcedon. This uniqueness prevents the dissolution of the vertical dimension into the horizontal through the dissolution of the love of God into the love of neighbor, which would be the formation of a ‘Christian atheism’.
Balthasar, Hans Urs von, and John Kenneth Riches. Theology: The New Covenant. San Francisco: Ignatius Press, 1989, 441.