Three Prefaces for Advent

At the Pro., Fr has been singing or saying the Advent Preface pro aliquibus locis, one of the last additions to the Roman Missal prior to the publication of the new Missal in 1969 - however, it is several centuries old, and first appears to my knowledge in the Paris Missal of 1738.

Here it is:

Præfátio de Adventu

Vere dignum et iustum est, æquum et salutáre, nos tibi semper et ubíque grátias ágere: Dómine, sancte Pater, omnípotens ætérne Deus, per Christum Dominum nostrum: 

Quem pérdito hóminum géneri Salvatórem miséricors et fidélis promisísti: cujus véritas instrúeret ínscios, sánctitas justificáret ímpios, virtus adjuváret infirmos. Dum ergo prope est ut véniat quem missúrus es, et dies affúlget liberatiónis nostræ, in hac promissiónum tuárum fide, piis gáudiis exsultámus. 

Et ídeo cum Angelis et Archángelis, cum Thronis et Dominatiónibus, cumque omni milítia cæléstis exércitus, hymnum glóriæ tuæ cánimus, sine fine dicéntes:

It is truly meet and just, right and availing unto salvation, that we should in all times and in all places give thanks unto thee, O Lord, holy Father, almighty everlasting God, through Christ our Lord, 

Whom to the fallen race of men as a Saviour thou, merciful and faithful, didst promise: whose truth would instruct the ignorant, whose holiness would justify the impious, whose strength would support the frail. Now, therefore, as it is soon that he shall come whom thou shalt send, and the days of our liberation shall shine forth, in this the faith of thy promises, we exult in holy joys. 

And therefore with angels and archangels, with thrones and dominions, and with all the heavenly hosts, we sing a hymn to Thy glory, saying without ceasing:

Like all prefaces, it has a protocol, or exordium addressing God the Father and confessing Him worthy of all thanksgiving; and an eschatocol or conclusion describing our joining with all ranks of the angelic hosts to sing the great hymn of victory (ἐπινίκιος ὕμνος), the Sanctus.

The body of the Preface rightly exults at this holy season of the Coming of our God: it praises the Lord for sending His Son to us fallen men as the long-promised Saviour: and instances His triple office of teaching, governing and sanctifying - that Christ our Lord brought the Truth to enlighten us, strength to strengthen us, and holiness to justify us.  (While there are many scriptural allusions, the only two verbal equivalences I've found are prope est ut veniat in Is. xiv,1 and quem missurus es in Exodus iv, 13.)

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Of course, throughout the world priests celebrating the Ordinary Form of the Mass have been using instead the modern first Preface for Advent, and for the last lead-up to Christmas will then switch to the second such Preface - though in my experience, at least once the Gospel readings start to mention St John the Baptist, many priests switch over to using the second one earlier, since it is an "easier" text, mentioning the joyful build-up to Christmas without dragging in the Eschaton.

Here's the Latin at least of these two modern effusions; the current ICEL translations are shoddy, and I'm not right now willing to make my own version:

Præfatio I

Vere dignum et justum est, æquum et salutáre, nos tibi semper et ubíque grátias ágere: Dómine, sancte Pater, omnípotens ætérne Deus: per Christum Dóminum nostrum.
Qui primo advéntu in humilitáte carnis assúmptæ, dispositiónis antíquæ munus implévit, nobísque salútis perpétuæ trámitem reserávit: ut, cum secúndo vénerit in suæ glória majestátis, manifésto demum múnere capiámus, quod vigilántes nunc audémus exspectáre promíssum.

Et ídeo cum Angelis et Archángelis, cum Thronis et Dominatiónibus, cumque omni milítia cæléstis exércitus, hymnum glóriæ tuæ cánimus, sine fine dicéntes:

Præfatio II

Vere dignum et justum est, æquum et salutáre, nos tibi semper et ubíque grátias ágere: Dómine, sancte Pater, omnípotens ætérne Deus: per Christum Dóminum nostrum.
Quem prædixérunt cunctórum præcónia prophetárum, Virgo Mater ineffábili dilectióne sustínuit, Joannes cécinit affutúrum et adésse monstrávit.
Qui suæ nativitátis mystérium tríbuit nos præveníre gaudéntes, ut et in oratióne pervígiles et in suis invéniat láudibus exsultántes.
Et ídeo cum Angelis et Archángelis, cum Thronis et Dominatiónibus, cumque omni milítia cæléstis exércitus, hymnum glóriæ tuæ cánimus, sine fine dicéntes: