A Great Reason for Christmas

Why is a truly Christian celebration of Christmas so important?  Note these ancient words from St Augustine:

For we are the sons of God, and although what we shall be has not yet been revealed, we know that when he appears we shall be like him for we shall see him as he is. For what are those treasures of wisdom and knowledge, what those divine riches, if not the one thing that can fulfill our longing? What are the great blessings of his goodness, if not the one thing that will content us? Therefore: Show us the Father, and all our desires will be satisfied.
Christ speaks both in us and for us when, in one of the psalms, he says to the Father: I shall be satisfied when your glory is revealed. For he and the Father are one, and whoever sees him sees the Father also. The Lord of hosts is himself the king of glory. He will transform us and show us his face, and we shall be saved; all our longing will be fulfilled, all our desires will be satisfied.
But this has not yet been accomplished; he has not yet given us the vision that will satisfy every desire; we have not yet drunk our fill of the fountain of life. So while all this remains in the future and we still walk by faith, absent from the Lord, while we still hunger and thirst for justice and with inexpressible longing yearn for God’s beauty, let us reverently celebrate the day he was born into our own servile condition.
Since we can as yet form no conception of his generation by the Father before the daystar, let us keep the festival of his birth of a virgin in the hours of the night. Since it is still beyond our understanding that his name endures for ever and existed before the sun, let us at least recognize his dwelling that he has placed beneath the sun. We cannot yet behold him as the only Son, abiding for ever in his Father, so let us recall his coming forth like a bridegroom from his chamber. We are not yet ready for the banquet of our Father, so let us contemplate the manger of Jesus Christ our Lord. (From a sermon by Saint Augustine, bishop, Sermon 194, 3-4: PL 38, 1016-1017)