I think the answer is twofold. First, what this scene seems to portray at essence -- forgetting the religious symbolism and biblical references -- is an effort of one individual to communicate something of profound importance to another individual. While the portrayals of that effort to communicate are so varied the story remains the same across all the varieties. How do we gain the attention of another, and have them hear our message, and listen openly to their response?
Of all the annunciations I have seen -- and I purchased at the Friary of San Marco in Florence a packet of postcards of sixteen of the most famous annunciations in Italy, which all unfold down to the floor -- the ones that most captivate me are those where Mary seems to reject the angel, or at least resist the call. These vary from outright hostility, to turning away, to shyly awaiting further information. The theme of the reluctant prophet, going back to Jonah and Moses, is fascinating to me: deeply human and honest about the unwillingness of all of us to trust a call, or to be willing to take on tasks we do not think we are up to.
The annunciation story in the Christian bible contained the dialogue between the angel and Mary. And yet they also speak to everyone: because who has not been asked to truly listen, and not failed? And who has been asked to take on what for them seemed liked a monumental task that they were were quite certain they were incapable of completing or completing well, and not resisted?
Simone Martini and Lipp Menni (1333), Florence, Uffizi
Fra Angelico (1432-33), Cortona
Fra Angelico (1438-45), Florence, San Marco
Leonardo Da Vinci (1472-75), Florence, Uffizi
Sandro Botticelli (1489-90), Florence, Uffizi
Mariotto Albertinelli (1497), Duomo, Volterra
Lorenzo Lotto (1534), Recanati