In today's reading (2 Sm 7:1-5, 8b-12, 14a, 16) we hear King David say, "Here I am living in a house of cedar, while the ark of God dwells in a tent!" The Lord does not need David to build Him a house, however. In fact, God says that, instead, He will build a house for David - and for you.
Don't build Me a house; I am building *you* a house.
What do we hear later in the Gospel? (Lk 1:26-38) We hear of the creation of the physical temple at the center of the city of God - the conception of the infant Christ by Mary's humble "yes".
It is reminiscent of another Old Testament swap that God made - don't you do this for me, I'll do this for you. When Abraham was ready to sacrifice his son, Jacob, he promises that God will provide the lamb. God stops Abraham before the sacrifice, because He is planning, indeed, to provide the sacrificial lamb.
Don't offer Me your son; I will offer Mine.
Don't forget that Bethlehem is the first step toward Calvary. The Temple was built on that day we celebrate with Christmas so that it could be torn down and rebuilt in three days. On that day, God provided the Lamb.