Christ is Emmanuel, God-with-us, Alpha and Omega, the Eschatos, the Fulfilment of all, the Word spoken to us last of all by God (Heb i, 1-2). His Incarnation is the End and Completion of all. Christian worship is not merely a happy remembrance of past events (what a Protestant notion), nor but a glance toward the last things (the Eschaton, or more properly, ta eschata), but an immersion in Him Who Is, the Eschatos, namely, Our Lord Jesus Christ, the one Liturgist, the Leitourgos (Heb viii, 2) – trust no other! – in Whom we have a participation in the economy of salvation, in His mighty acts past, present, and to come.
For this reason, amongst others, the churches of the Byzantine tradition very often address their prayers to "Christ our God", whereas the Holy Roman Church keeps in the main to the still older tradition whereby prayers are addressed to God the Father. The insights of both East and West coincide, of course, when considering the centrality of the Enfleshment of the Divine Word. To-day's Collect at Mass, for the 31st of December, the 7th day of the Christmas Octave (found in both the Hadrianum and the Leonine Sacramentary, and thus dating back to the 7th century at least), repays much careful consideration in its magnificent encapsulation of this mystery:
Omnipotens sempiterne Deus, qui in Filii tui nativitate tribuisti totius religionis initium perfectionemque constare, da nobis, quæsumus, in ejus portione censeri, in quo totius salutis humanæ summa consistit. Per...
This may be rendered as:
Almighty everlasting God, Who hast given, in the birth of Thy Son, the beginning and end of all religion to consist, grant us, we beg, in His portion to be reckoned, in Whom the sum of the whole of human salvation doth consist. Through...
Similarly, but not quite so painfully literally, the new translation of the modern Missal englishes the Latin original thus:
Almighty ever-living God, who in the Nativity of your Son established the beginning and fulfilment of all religion, grant, we pray, that we may be numbered among those who belong to him, in whom is the fulness of human salvation. Through...
Note the Latin particularly: in Filii tui nativitate... totius religionis initium perfectionemque constare – the beginning and the perfection of all religion consists in the birth, or, rather, in the Incarnation, of the Son of God Almighty and Eternal. "Nativity", "birth" must be understood in the sense of the first unveiling of the Incarnation to human eyes (though known first by faith, then by revelation, and then by joyful interior awareness to the Most Holy Virgin at the Annunciation; and a little later to St Joseph), when Christ was born at Bethlehem, the "House of Bread". The Incarnation is totius religionis initium perfectionemque; just as in due measure the Eucharistic Sacrifice, whereby He, the Eschatos, becomes present to us, in an extension of His Incarnation as it were, is the "source and summit" of Christian worship:
...Liturgia est culmen ad quod actio Ecclesiæ tendit et simul fons unde omnis ejus virtus emanat. ("...the liturgy is the summit toward which the activity of the Church is directed; at the same time it is the font from which all her power flows.")
— Sacrosanctum Concilium, 10.
While in many and varied ways God spoke to us through His prophets of old, in the fulness of time He spoke to us, lastly, in His Son, His Word, Who for us took flesh, and became the Verbum abbreviatum, the Infinite confined in a Body, God the Son become the Son of Man. (Like the TARDIS, Christ is "bigger on the inside"...) As St John of the Cross rightly asks, why seek for some further or other communication from on High, when the Most Highest has spoken His Eternal Word to us? In Christ is all the fulness of Divinity; He is the definitive revelation of the Father.
But there is still more to consider in this Collect, for its first phrase is paralleled by its last: in quo totius salutis humanæ summa consistit – in Whom the sum and height and total of all of human salvation is found, exists, consists. For there is no other salvation than that found in Christ our God. Note the repetition of the verb: constare, consistit. Note the repetition of totius. Note the paralleling of perfectionem and summa.
Religion, in St Augustine's words, is that by which man is "re-bound" to God, as if derived from re-ligare. Hence, if the Nativity of Christ, the birth of the Incarnate God, is the beginning and the end of all religion, all re-connecting of man to the All-Highest, then of course in Him and His Nativity is found likewise the totius salutis humanæ summa. These terms again parallel each other.
Therefore, what we pray for is detailed in the middle of the Collect: that we may have some part and share in Him. Glory be to Christ, in Whom all glory is to God on high, and all peace to men of good will, those who enjoy His grace and favour.