Instead she takes the tune the angel gives her, the tune so different from the one she had in mind, and begins to hum it to herself. It's much the same song the prophet Isaiah sang centuries before, when he had a vision of the spectacular holiness of God, and of his own spectacular unworthiness to be anywhere near God. But God sent an angel to change his tune. We can think of a thousand excuses for not offering our services. Greed is good.
Guilt is bad.
We're not in control. Life is not as it should be. Our song is way off key. There are risks involved in taking up Mary's song, in accepting Mary's child into our lives, in allowing ourselves to be impregnated by that same Spirit whose word both blesses and terrifies. There are no scripts, no guarantees.