In Advent of 1962, Karl Barth was invited to preach in a prison. He chose as his passage the Magnificat, Luke 1:46-55, the song of Mary. In his sermon Barth remarked, "A house in which the weary and heavy-laden, the poor and needy who are really hungry live – that is, a house like the one in which we find ourselves – is the right match for Christmas." For Barth, if Christmas doesn't come to the poor house, rest assured it does not come at all.
It is crucially important that Gabriel did not appear to a queen. God did not make his entrance into the world through a family of means and social standing. The baby Jesus didn't come to the kind of family who could send their kid to Harvard. Instead, Gabriel appeared to a young girl from a podunk town in a Galilean backwater. The angel makes it clear that she has found favor with God, and so after a clarifying question Mary responds, “I am the Lord’s servant. Let it be with me just as you have said ” (Luke 1:38 CEB). The angel departs, and Mary rushes out to pay her cousin Elizabeth a visit. After Elizabeth pronounces a blessing over her (the angel's words and Elizabeth's words make up the majority of the "Hail Mary" prayer, popular in Roman Catholicism), Mary bursts into celebratory soliloquy: "Μεγαλύνει ἡ ψυχή μου τὸν Κύριον.../Magnificat anima mea Dominum../My soul magnifies the Lord..."
Mary hymns her joy at the God who saves, who looks with favor upon the lowly, who shows mercy and strength as he turns the world upside down: filling the hungry with good things and sending the rich away empty. Somehow this mercy has reached a climax right here in this pregnancy; somehow this is God definitively coming to the aid of Israel and fulfilling his promises to Abraham in a way that opens up his mercy not only to Israel but to everyone who honors him as God.
Mary's song would not be very interesting - indeed it would be pretty boring - if it was just a proof text that we're supposed to love the poor, or that God cares about the poor, or that we're supposed to vote a certain way or think a certain way or live a certain way. The song may very well have implications for some of these things - and we should take it seriously where it does - but it happily goes much deeper.
John Wesley once remarked that "religion must not go from the greatest to the least, or the power would appear to be of men." Here it isn't so much "religion" as it is God who moves with clarity of purpose, starting at the bottom: with a young woman in a society where youth and femininity were not valued, with a poor young woman in a society in which social mobility was rare - especially for women who don't marry rich. Mary married a construction worker.
But Gabriel comes right there, to this woman, and announces this birth. No man seeking to establish a kingdom would have done so in this way. But God does, because God is not bound by the rules of conventional wisdom or polite society or status quo politics or poverty and wealth. God exists outside all of these things. And because God exists beyond these things, when God steps into the midst of them we have real, material reason to hope that these things might be redeemed.
And so this is the meaning of Christmas: not a moral command, a mere cute story or a bit of advice, but God, for the love of his creatures, steps into the world - and now the world cannot stay the same.