This is a very rare occurrence. In fact, since 1864, it's only happened FIVE times. 2016 will bring that total to six, and it won't happen again for another 141 years (that's 2157 for those doing the math). Thus, in our lifetimes (and in our children's lifetimes) this is a rare opportunity. When we participate in the Triduum Liturgy, not only is it a connection between the Last Supper on Holy Thursday and the Resurrection on Easter Sunday but a confirmation of the Annunciation - a full circle of Salvation History!
That all being said, the Church chooses to "transfer" celebration of the Annunciation to a different date when this sort of thing happens. That's explained here:
The Annunciation celebrates a deeper truth than Angel Gabriel giving Mary the heads up about Jesus; it celebrates the Incarnation which was a direct result of Mary's Fiat. Christ became incarnate specifically so Good Friday could happen which is why having the Annunciation fall on Good Friday is so poetic.
Sometimes, it's very hard for us to reconcile that those two Persons are, in fact, the same. And yet, it is true. Christ became incarnate within Mary precisely so He could grow up to meet the Cross on Calvary. Thus, the Annunciation (also celebrating the Incarnation) is inextricably linked to Lent. We would do well to remember in our meditations the great Sacrifice that began with this very Feast.
Mary's Passion, too, began here. After all, when she consented to bear God within her, she wasn't just consenting to become a mother in a way she didn't understand. She was also consenting to the immense suffering she knew would come with such a request. While she may not have known her Beloved Son would be so cruelly murdered, I have little doubt she understood that He'd be the Sacrifice which would ransom humanity.
Indeed, we know Our Lady was raised in the Temple. She would have known the Old Testament scriptures through and through. In fact, she is many times pictured with scrolls or kneeling / standing behind a pulpit with prayer meditations. Thus, because of her intimate knowledge of Scripture (the non-incarnate Word of God), it would be easy to surmise that she had a pretty good idea that once incarnate, the Word would fulfill the many passages that prophesied His Passion and Death.
This connection is one of the reasons I love John William Waterhouse's painting of the Annunciation so much:
Purple, folks... the color of both Advent and Lent (keenly joined thematically through the Annunciation). Purple, as I always tell my students, is the color of sacrifice. Why? Because way back when, the dye for making that color was so expensive that only the very rich could afford it. Hence why the Romans were always dressed in purple - to signify their power.
To scrimp and save for such a color would require intense sacrifice. This is why purple has historically been reserved for (and indicative of) royalty. It's also why the Church chose to utilize this color for Advent and Lent, our times of penitence through sacrifice.
Anyway, Angel Gabriel isn't just bringing Mary joyous tidings of Divine Motherhood. Instead, he is bearing such awesome news with equally awesome humility as the glorious honor is an equally heartbreaking burden. (***Fun Note: In the Jewish language, the word "honor" is "kabad/kabed" which actually translates to something akin to "glorify and burden." So thinking back to the 10 Commandments the Jews were given, #4 - Honor thy father and mother - takes on a whole new meaning. I detailed how Jesus could possibly reconcile these two through His treatment of Our Lady here.***)
Waterhouse's stunning portrayal of Our Lady is just so incredible. She has her hand over her heart, her other hand on her head, and this look of gentle contemplation on her face. This must be the moment just before her "Fiat." She's processing what Angel Gabriel has said, and Gabriel, along with all of Heaven, awaits her response with bated breath.
Will she take up the obedience that Eve let fall? Will she consent to hand her very body and soul to God for the Salvation of humanity?
***Also, another fun aside, in Waterhouse's painting, there is a spindle and distaff of yarn next to Our Lady. Symbolically, the spindle and distaff represent the present life and the spiritual life. The spindle, ever spinning, is indicative of life on earth while the distaff moves up to remind us of the heavenly plane. I can't be sure, but I can't help but wonder if Waterhouse wasn't suggesting that Our Lady is the pure white thread connecting humanity (through her Fiat) to Heaven.
I really do love me some Sacred Art.