The Propers of the Office and Mass for the majority of Sundays and Feast days in the West are remarkably conservative in that most of them are direct quotations from Scripture. Later monastic and ecclesiastical poetry is not foreign to the services, however, and is always sprinkled throughout them. Here, for instance, is a sampling of extra-biblical poetry and prayers in the Propers for the Feast of the Annunciation:
Vespers:
Antiphon on Magnificat
Blessed art thou Mary, who hast believed; * there shall be performed in thee the things which were told thee from the Lord.
Antiphon on Psalm
The Savior of the world shall arise as the sun: * and shall come down into the Virgin’s womb, as the showers upon the grass.
Matins:
In Nocturn I
℟. Receive the Word, O Virgin Mary, which is brought thee from the Lord by an angel: conceive and bear him who is both God and man: x That thou mayest be called blessed among all women.
℣. For thou shalt bear a Son, yet shalt thou remain unspotted in thy virginity: thou shalt bring to pass great things, and shalt be a Mother ever Virgin. x That thou…
In Nocturn III
℣. God hath chosen her and preferred her.
℟. He hath made her to dwell in his tabernacle.
℟. O holy and spotless virginity! I know not how to praise thee: x For thou hast borne in thy breast him who the heavens cannot contain.
℣. Blessed art thou among women, and blessed is the Fruit of thy womb. x For thou hast…
Blessing: May the Virgin of virgins whose Feast we are keeping intercede for us to the Lord.
℟. Rejoice with me, all ye that love the Lord, for although I was lowly I pleased the Most High. x And from my womb I have brought forth God and man.
℣. All generations shall call me blessed, for the Lord hath regarded the lowliness of his handmaiden. x And from my womb…
Mass:
The Collect
O God, who didst ordain that thy Word should take flesh in the womb of the Blessed Virgin Mary at the message of an angel: grant that we, thy suppliants, who believe her to be indeed the Mother of God, may be aided by her intercession before thee; through the same…
The Secret
Stablish in our hearts, we beseech thee O Lord, the mysteries of the true faith: that like as we acknowledge thy Son conceived of a Virgin to be very God and very Man: so by the power of his life-giving Resurrection we may be found worthy to attain unto everlasting gladness; through the same…
The Postcommunion
We beseech thee O Lord, pour thy grace into our hearts: that as we have known the Incarnation of Christ thy Son by the message of an angel, so through his Passion and Cross we may be brought unto the glory of his Resurrection; through the same…
As you can see, even the “original” works of later Christians which made it into the Propers are highly informed by biblical language and phraseology. And in the Mass of Annunciation, only the Collects and prayers are of later composition, the other Proper chants coming entirely from Psalm 45, Isaiah 7, and Luke 1. This pattern of using mostly Scripture (and mostly from the Old Testament) for the sacred chants of Christian liturgy demonstrates the confidence and surety of the Christological (and by derivation in this case also the Mariological) interpretation of the Scriptures.