What has to be brought together today is the justified concern for the future of mankind, which has more than ever been entrusted to human capacity and responsibility, and the inalienable demand that every individual think here and now of his relation to God and his eternal salvation. Man must give himself completely in two directions: the horizontal “forward” and the vertical “upward ”. And this should be accomplished in such a way that each direction does not hinder the other but on the contrary furthers it.
But how is this possible? How could a person such as the marxist [sic], who is absorbed completely in the service of future mankind’s well-being, have the time and desire to pray and to collect himself in God? On the other hand, how could someone who practices Eastern meditation and submerges himself in the Absolute dedicate himself completely to his earthly task?
The vertical and the horizontal cross only in the Cross of Christ: only in him is the dedication to mankind perfectly one with the immediate contact with the Father’s will. Why? Because the will of God for which Christ listens in prayer sends him always anew into the world and its distress, not with merely human programs, but with a plan of salvation that can be thought and realized only by God. Action alone is not enough; even in Jesus’ life on earth it did not reach its goal. Prayer is not enough; it points at first always to action but finally to the third thing which alone leads to the breakthrough, the great suffering that is like the synthesis of action and contemplation: the bearing of the unbearable guilt of the world which had barred the access to God forward as well as upward. The door is now open in both directions.
Forward: what good are the marxist [sic] plans for the future if humanity cannot be essentially changed and if the innumerable past generations remain unredeemed? The Christian works for change in the world in the hope, initiated by Christ, of his return, the hope of the coming of the kingdom of God which will transform everything and integrate into itself every effort for the good.
Upward: what good are all the ecstasies and submersions practiced in Eastern techniques if they do not encounter the living Heart of God, the absolute love that proved itself in the Cross of Christ, a love with which we never become identical but which gives us a share in itself in the Holy Spirit?
Man remains stretched between heaven and earth without ever bringing the two dimensions of his existence to a final harmony by his own power. Does this not show that from his creation he has been designed for the Crucified and Risen One in whom his restless heart finds rest?
The same point can be expressed even more simply with the gospel: the two main commandments, the love of God and the love of neighbor, become one only in the One who is at the same time God and man. This incomparable fact is and remains the center of Christian apologetics.
Hans Urs von Balthasar, A Short Primer for Unsettled Laymen (1980) - in chapter titled Why Still Christianity
In his discussion of the "horizontal" and "vertical" dimensions of faith—that is, service of humanity and worship of God, Balthasar concludes that they can only be brought together in the person of Jesus and his Cross. In the course of sketching his larger argument, he makes this wonderful point about both the limits and the potential of the "horizontal".