The "Great O" which we sing today contains the only phrase in an O Antiphon which is traced exclusively to the New Testament:
O King of the Nations, and their desire, the cornerstone, who makes both to be one: Come and save mankind, whom you formed from clay.
The phrase "who makes both to be one" appears to be a reference to St. Paul's letter to the Ephesians where he describes the reconciliation between the Jews and the Gentiles. That Christ came to bring salvation to all, not merely the people of Israel and their descendants, is indicated in this antiphon. Just as the previous antiphons show the clear relationship between the Old Testament covenant and Christ's fulfillment of that promise, this antiphon carries the fulfillment a step further as it is extended to those traditionally excluded from the promises made to the Israelites and their heirs.
As we intone this antiphon we draw ever closer to the manger in Bethlehem. Fellow travelers along the road ask us where we are going and we reply that the King awaits us. He does. The real question is, perhaps, do we believe that he is our King? Do we act as though he is the King of our hearts? Let us, these last days of Advent, make known that the desire of the nations is indeed the desire of our hearts. Let our actions and our words speak of him and let us invite others to journey with us as we approach the newborn King in the humble manger of our hearts where He is born anew each year.