In Sunday’s Old Testament reading (Samuel), David realizes that there’s something not right when he has a house but God’s Ark is in a tent. So he asks Nathan about building a house for God. Nathan (not checking with God first) says “go ahead.” But when Nathan checks in with God, he finds out that God has something very different in mind.
Acting on their own, good people with the best of intentions can (and do) get it wrong. So God reminds them who really does the building. And then God tells them about his plan, which involves a very different kind of house.
Where the Old Testament reading is all about “what” will happen, Sunday’s Gospel Luke) is all about “how” God’s plan will happen. David is told about God’s plan. Mary is told about God’s plan - and is asked to trust God and to be a part of that plan.
Mary says “yes.” And everything changes.
Readings for Sunday: http://www.usccb.org/bible/readings/122114.cfm