The Advent Code

It is time that the truth be made known more widely. For centuries, this knowledge has been handed down within an elite group, the "liturati" (the "liturgically literate"). The fact is, this code is hidden in plain sight in the official prayer of the Church! Amazingly, you yourself have most probably been singing its secret message since childhood, because it has found its way into the classic Advent hymn, O Come, O Come, Emmanuel: It is an acrostic in which each verse contains a single piece of the Code, even though the Code only appears when the hymn or the antiphons upon which it is based are sung in Latin. Today, the Code is alluded to in the Alleluia verse of the day's Mass and in the antiphon before the Gospel Canticle in the Evening Prayer of the Liturgy of the Hours during the eight days before Christmas.
Behold, I reveal to you the Advent Code, hidden in plain sight in the "O" Antiphons of Advent (which you will also find in our Christmas novena on YouTube):
O WISDOM (Sapientia) of our God Most High, ordering all things mightily and sweetly…Come!
O ADONAI, Leader of the House of Israel…Come! (Adonai—Hebrew, usually translated "Lord")
O ROOT (Radix) of Jesse…Come!
O KEY (Clavis) of David…who open and no one closes…Come!
O RISING SUN (Oriens), splendor of eternal light…Come!
O KING (Rex) of Nations, for whom they have been yearning, Cornerstone who unites in perfect union…Come!
O EMMANUEL…awaited of the nations, Redeemer of all, Come!

Now, the all-important key to the Advent Code.
Part the First
Take the first letter of each key word (in bold). The result will be SARCORE.
Part the Second
Leonardo-like, reverse the order of the letters: EROCRAS.
Part the Third
Use your high-school Latin to discover the two words ERO and CRAS.
Ero: first person, singular, future tense of the verb "esse" (sum, esse, fui, futurus): to be.
Cras: tomorrow

The Code has been broken! By the end of the antiphons, the message appears, "Tomorrow, I will be."