And Zacharias said unto the angel, Whereby shall I know this? for I am an old man, and my wife well stricken in years.I don't know why I didn't see this before: Whereby shall I know this, as opposed to How shall this be? One is an epistemological question, the other a metaphysical, one a question about personal psychology, the other about divine reality.
Then said Mary unto the angel, How shall this be, seeing I know not a man?
I suppose this is something that sharper tools in the shed have seen all along, but I'm still marveling over the richness of biblical texts that can say so many different things to so many different people with such an economy of words. Being versus knowing, humility versus skepticism; Mary humbly accepts that God's will is just a manifestation of how things are, while Zachariah wants, principally, to be given a satisfactory account of how things will be.
A particularly humbling text for the philosopher, most of whom deserve a more permanent version of Zachariah's punishment.