According to Tradition, 25 March is both the beginning and the end of the earthly existence of Our Lord Jesus Christ. Conceived on this day in the immaculate womb of Mary, He also expired on the cross on Good Friday some 33 years later (that's why it's also the feast day today of the good thief, St Dysmas).
It is no accident. The Word became flesh in order to redeem us, and that redemption goes through the cross. From the very beginning of His pilgrimage on earth, the Lord Jesus says to His Father, "Sacrifice and oblation Thou willest not, but a body Thou hast formed for me" (Ps. 39), and it is through that sacred Body that we are saved.
Our Lady pronounced her fiat at the Annunciation, but she pronounces it again on Calvary, accepting her mission, and all it entails for her. I was privileged to make my solemn monastic profession on this day 28 years ago. That year 1989, it was Holy Saturday, and so my solemn vows were pronounced during the paschal Vigil. That ceremony marked me for life, for it impressed on me that it is only by dying that we shall rise to new life, and that Mary is there at every step, teaching me to say unceasingly "Fiat".