Of all the treasures that have come down to us from the history of Christian spirituality, of all the various ways of prayer, the one that I think speaks most clearly of the mystery of Advent is the ancient monastic practice of lectio divina, or sacred reading. The reality, of course, for most Christians since the time of Christ has been that they could only ever hear the scriptures, not read for themselves, because until fairly recently most people couldn't read. And so in the monastery, every morning, a group of monks would gather together in the chapel around the lectern and a single monk, who could read, would come forward, approach the book and bow. Then he would find the passage set down for the day, and, very slowly, he would begin to read the story of God's words in the world. When he had finished, he would bow again and back away from the lectern. After a short silence he would again approach and read again the same passage. He would do this, over and over, until there was nobody left in the chapel to hear. Each monk, as he heard the word that he needed to reflect on that day, would silently leave, the Word having invaded not only his ears and his brain but his whole body. Throughout the day, the monks would chew it over – ruminate on the Word they had received until it literally transformed them from within. We don't listen like that any more, since words to we folk of a more literate age have become black marks on a page that we scan at increasingly high speed, we've lost the art of allowing God's Word to sink into us at the level of our flesh and blood.
The most scandalous message of Advent comes through loud and clear today as Christmas approaches: despite everything, the angel tells us, God's true home is within us, God desires us and God chooses to be most fully revealed in us, despite all the violence, all the corruption and all the trickiness of human hearts, God chooses to be at home in us. "My gospel," Paul says in the final verses of his letter to the Romans, "The heart of the good news that I share with you - which has been completely misunderstood all through the ages, this mystery that I am giving you is going to change the whole world."
What mystery? What's been so completely misunderstood? According to St Paul it's this: that God is not up there or over there - Do you not know, he asks almost incredulously, that your body is a temple of the Holy Spirit who is in you? That God is incarnate in you.
It's what David finds out in our first reading. David's intentions seem honourable enough – 'here I am, living in a palace – it's not right that God should live in a tent'. It's what we do ourselves – let's do up the church, plant a garden, decorate the worship area – it's God's house and we want to praise God in it. But God puts David straight – you've got it the wrong way around – you don't build me a house – instead, I'm going to make a house out of you. It's a play on words – David is thinking about bricks and mortar but God has got something else in mind - a lineage, flesh and blood. It might seem strange that in this last week of Advent we've left the sweeping visions of Isaiah to hear about David's building plans but here's the point – God doesn't plan to be confined to a building we visit on Sundays, or to a book on a lectern – or even to the bread and wine of the Eucharist – God doesn't even intend to be confined in the heavenly hereafter – God plans to live in us.
This isn't new or radical thinking about God. St Paul knew it, the writer of the book of Revelation knows it when he writes, 'And I heard a loud voice from the throne saying, "See, the home of God is among mortals. He will dwell with them; they will be his peoples, and God himself will be with them"'.  And the monks who allowed God's Word to seep into them in the practice of lectio divina also knew it. The people of Israel knew it in their earliest writings, in the book of Genesis that tell how God breathes life into the dust of the earth, how God walks with human beings in the cool of the evening – but along the way we forget, we come to think of God as remote from us, as being up there or over there, or in a different dimension.
We forget so much that by the time of the prophet we call 2nd Isaiah the people of God have to be jolted awake by being called 'the people who walk in darkness'. Even we Christians forget, when we elevate Jesus so highly that we want to make him the only human being in whom God is revealed. When we so emphasise that God is present in Jesus of Nazareth that we fail to see the presence of God in the people we live with, that we fail to see the suffering of God in the faces of street children or homeless men; the God who is incarnate in those we fear just as much as in those we love. When the Incarnation of God is an event that we think only happened 2,000 years ago in a stable in Bethlehem, that runs the risk of making Christmas too safe, mistaking the cuteness of the nativity scene or the sublime architecture of a cathedral for the utter scandal of God choosing to be revealed amongst the scruffy and the unclean and the dangerous.
And so we come, in the fourth Sunday of Advent, to Mary. Writer Madeline L'Engle reminds us of the legend that Mary was not the only or the first teenage girl that the archangel Gabriel visited – just the first one to say yes.
"Are you sure? (L'Engle writes)
but I'm unworthy -
I couldn't anyhow -
I'd be afraid. No, no,
Do I have to answer now?
I don't want to say no-
Let me have a few days to think it over."
Sorrowfully, although he was not surprised
to have it happen again,
the angel returned to heaven." 
What makes Mary extraordinary, according to this legend, was her willingness to stand face to face with an angel in all its scary splendour and open herself to God at work in her, the gift of God's Word becoming flesh and dwelling among us... As William Willimon writes, 'incarnation means that the God who stands outside of time also enters into time, the God who is infinite becomes finite, the God who is all-powerful becomes all-vulnerable. The God whose womb bore the world now grows molecule by molecule in Mary's womb to bear the good news of peace on earth'. 
I think Madeline L'Engle gets it about half right – but it's not just teenage girls in Nazareth who get a surprise visit from Gabriel – we all get the invitation to open ourselves up, to become pregnant with God's Word – I think, over and over –such an intimate, gentle breath of angels' wings that we often don't hear. The beauty and the wonder of Mary is that she stands for all who are powerless and vulnerable, the 'yes' she gives is so incongruously self-assured – she stakes everything she has and everything she is on the utterly preposterous notion that God's Word taking shape within her is going to be sufficient not only for her but for the whole world. Maybe you have to be poor and powerless to take a risk like that – how often, I have to ask myself, have I refused to let God's Word find a foothold in my life because I think there's more security or better prospects in following my own agenda? The gospel of Mary is a gospel of challenge.
In a slightly grotesque image, St Augustine claims that when Mary says 'yes' she is impregnated by the Holy Spirit through the ear. Maybe he could have thought that metaphor through a bit better, but what he means is that just as Mary conceives through hearing and responding to the Word, so too new life comes to us when we listen to the Word. When we hear and allow ourselves to be transformed by the Word, we become "pregnant" with the Spirit. The scandal of Advent repeats itself - Christ takes on flesh in you and me.