Rorate Caeli

March 25, date of the Incarnation and Passion: Annunciation and Good Friday: Popule Meus, quid feci tibi?

O holy God! O holy Strong One! O holy Immortal One! Have mercy on us.

As is well known, many early Fathers and much of the faithful believed that the first Good Friday fell in the solar Roman Calendar of its time (the Julian calendar, later slightly refined at the order of the Council of Trent to take account of the actual seasonal changes) on March 25, the same day of the Annunciation. This has taken place this year, and it is a rare event: it will only happen again in the year 2157, when we will be long gone from this earth:

[T]raditionally the conjunction of the two dates was considered to be both deliberate and profoundly meaningful. The date of the feast of the Annunciation was chosen to match the supposed historical date of the Crucifixion, as deduced from the Gospels, in order to underline the idea that Christ came into the world on the same day that he left it: his life formed a perfect circle. March 25 was both the first and the last day of his earthly life, the beginning and the completion of his work on earth. The idea goes back at least to the third century, and Augustine explained it in this way:
He is believed to have been conceived on the 25th of March, upon which day also he suffered; so the womb of the Virgin, in which he was conceived, where no one of mortals was begotten, corresponds to the new grave in which he was buried, wherein was never man laid, neither before him nor since.

This day was not only a conjunction of man-made calendars but also a meeting-place of solar, lunar, and natural cycles: both events were understood to have happened in the spring, when life returns to the earth, and at the vernal equinox, once the days begin to grow longer than the nights and light triumphs over the power of darkness. Here's Bede explaining some of the symbolism of this latter point:

It is fitting that just as the Sun at that point in time first assumed power over the day, and then the Moon and stars power over the night, so now, to connote the joy of our redemption, day should first equal night in length, and then the full Moon should suffuse [the night] with light. This is for the sake of a certain symbolism, because the created Sun which lights up all the stars signifies the true and eternal light which lighteth every man that cometh into the world, while the Moon and stars, which shine, not with their own light (as they say), but with an adventitious light borrowed from the Sun, suggest the body of the Church as a whole, and each individual saint. These, capable of being illumined but not of illuminating, know how to accept the gift of heavenly grace but not how to give it. And in the celebration of the supreme solemnity, it was necessary that Christ precede the Church, which cannot shine save through Him... Observing the Paschal season is not meaningless, for it is fitting that through it the world's salvation both be symbolized and come to pass.

As Bede says at the end here, this dating is symbolic but it is not only a symbol; it reveals the deep relationship between Christ's death and all the created world, including the sun and moon and everything on earth. According to some calculations 25 March was also considered to be the eighth day of the week which saw the creation of the world (for more on that, see this post), as well as the date of certain events from the Old Testament which prefigured Christ's death, including the sacrifice of Isaac and the crossing of the Red Sea. It is the single most significant date in salvation history... .0

The Red Sea... which Christ Himself parted, taking His People out of Egypt. And yet we killed Him. Have mercy upon us, Son of God and Son of Mary!

(Note: the Annunciation will only be celebrated on April 4, after the end of the Easter Octave.)