In Christ, according to Christian belief, God himself has entered into history; in him the last things have already begun, the end time is already at hand, and the pilgrimage of the nations to Mount Zion has become God’s pilgrimage to the nations. Universalism is no longer just a vision of something that is to come, but must, in the now of the end time, be transformed by faith into concrete facts.
The Church Fathers understood the Christ-event as a mystery of union. Sin, on the other hand, was disunion – a division into the egoism of each separate individual; it was a “Babylon” of idolatry. Faith, on the contrary, means tidings of a unity that transcends all boundaries: “One Lord, one faith, one Baptism, one God and Father of all, who is above all and through all and in all” (Eph 4:5).
It is not difficult to comprehend the fascination that was aroused by such tidings, the hope that was awakened…The preaching of Jesus was not, at first, a preaching of the Church of the nations, but a proclamation of the Kingdom of God. Theologians have long accorded too little recognition to the astounding fact that Jesus’ preaching of the Kingdom, which experienced its first setback in his Crucifixion, but was revitalized after his Resurrection, was definitely rejected by Israel, and that from that time on his message can exist only in the form of a mission to the nations. This mission to the nations we call Church…She arose as the new form of the covenant, which at bottom can claim to be no different from Israel’s holy mission” to be a light for the nations by her witness to the Passion and her service of love.
From: Kirche in der ausserchristlicher Welt, pp. 26ff.