Pope Benedict preached on Psalm 2 and the phrase, "The Lord said to me, you are my son, this day have I begotten you.":
But there is more: in Jesus Christ, the Son of God, God himself became man. To him the Father says: “You are my son.” God's everlasting “today” has come down into the fleeting today of the world and lifted our momentary today into God's eternal today. God is so great that he can become small. God is so powerful that he can make himself vulnerable and come to us as a defenceless child, so that we can love him. God is so good that he can give up his divine splendour and come down to a stable, so that we might find him, so that his goodness might touch us, give itself to us and continue to work through us. This is Christmas: “You are my son, this day I have begotten you.” God has become one of us, so that we can be with him and become like him. As a sign, he chose the Child lying in the manger: this is how God is. This is how we come to know him. And on every child shines something of the splendour of that “today,” of that closeness of God which we ought to love and to which we must yield it shines on every child, even on those still unborn.(The full text may be found at http://www.theglobeandmail.com .)
Luther's sermon is not dealing with Psalm 2, but the Nativity, and the phrase from Benedict, " he can make himself vulnerable and come to us as a defenceless child, so that we can love him," is reminiscent where Luther says that God's majesty is not what we contemplate in the Nativity but his utter human vulnerability. In the Incarnation, the Son of God becomes pure gospel. "Trust him! Trust him!" Luther cries. It is no wonder that Christmas is many Christians' favorite festival. Here we have a picture of God who comes to us in complete defenselessness, utter dependence, and yet to save. That God thinks enough of us to come to us is awesome on its own, but that God trusts us to be dependent on human parents is itself perhaps even more incredible.