We know that at the moment of the Immaculate Conception, the New Testament silently begins. It begins in a hidden way, without any fiat from Mary or her mother. It begins entirely with grace, as everything begins.
The Kingdom of Heaven at Mary's Immaculate Conception was smaller than a mustard seed, less noticeable than a pinch of yeast, surrounded by the darkness of a womb - a darkness that did not overcome it. And yet from this small and seemingly insignificant beginning, the Kingdom has come among us in power and clarity.
Fourteen or so years later, the Kingdom has another small and hidden beginning. John the Baptist is conceived before Our Lord begins to live in the Virgin's womb. And while we know that Mary says yes to God when the angel appears to her, we know that Zechariah breathed out a kind of no. He responds to Gabriel with a doubt.
In that doubt is the antithesis of Faith; in that doubt is the kind of No that can undo the Kingdom. And in that doubt is the last word Zechariah speaks until his lips are free to affirm God's plan at the birth of Zechariah's son. "His name is John" is Zechariah's Yes to the absurdity (in human terms) of the Providence of the Lord. His first words in nine months, his first utterance after his penance of being unable to speak are a surprising and even shocking "Yes". It is his way of saying, "I renounce my selfish and personal claim to the identity of my only son; I offer him up to this new order which is breaking through, to the glory we are beginning to glimpse behind a torn veil."
And then when Our Lady says Yes - when she gives her fiat - her action is less active than it is passive. It is an action that allows, that suffers, that permits God as the active source of grace to work his wonders through her, through His Son, and through us.
If we don't have the courage to say Yes, may we at least have the grace to stop saying No.