I have for a number of years preached that March 25th is misnamed in the Church Kalendar-- it is most importantly the actual Feast of the Incarnation. When we refer to Christmas as the Incarnation, we are strongly implying that "the Word became flesh and dwelt among us" at the moment of His human birth. That not only bad theology, but dangerous.
The Word became flesh and dwelt among us first as a zygote and then as an embryo-- the Creator of the entire universe allowed Himself to become just a few tiny cells within that universe, and to gestate and grow within the womb of the Blessed Virgin Mary, and to be born, fully human and yet fully God. If we call the Feast of the Nativity the "Incarnation" (as too many do), then there is no reason not to allow abortion-- if Jesus became human only after His birth, then, by definition, embryos are not human.
The Nativity remains important-- it is when the Incarnation was announced to the Jews, via the shepherds, just as the Epiphany is important because it commemorates the Incarnation being proclaimed to the world at large, via the Magi/"three kings". But March 25th, when that young girl, frightened by the Archangel, frightened by the enormity of what was being asked of her, still said "yes", still said Ecce ancilla Dómini; fiat mihi secundum verbum tuum (Behold the handmaid of the Lord; be it unto me according to thy word)... that is the true Feast of the Incarnation. Et Verbum caro factum est, et habitávit in nobis! (And the Word was made flesh, and dwelt amongst us.)
Also important to us is to remember the words Mary spoke, and to make them our own. "I am the servant of the Lord; be it unto me according to thy will." Our culture teaches us that what we want is most important-- from Burger King's "Have it your way" through McDonalds' "You deserve a break today!" to my least favorite, L'Oreal's "Because you're worth it!". But we shouldn't always have it our way, and we're not worth it. We're each of us broken, each of us sinful. Many of us are indeed 'doing the best that we can', but that best, sadly, isn't good enough. If it were, God would not have to have humbled Himself to become a mere human embryo, to be born through blood and pain into a human life ending in a horrible, tortured death, and solely out of love for us.
In response to such immense love, what other response can we possibly give, other than "Be it unto me according to Thy word."?