In the early church, Easter, not Christmas, got the most attention. Easter, after all, focuses our attention on the death and resurrection of Christ—the heart of the Christian gospel.

Christmas’s status began to change, though, in the fourth century—perhaps not unrelated to the Nicene controversies and the attention they drew to Jesus’s origins.

We see a glimpse this transitional period in Augustine’s writings. In his correspondence with Januarius from around the year 400, especially Letter 55, Augustine distinguishes between Easter, which he says is a sacrament, and other feasts, like Christmas, which are better characterized as “commemorations” of historical events, akin to the feasts of martyrs.

The difference is that, in a sacrament, Christians not only remember but actually participate in the transitus the event signifies. In Easter, Christians join in the transitus of death to life. Pointing to Romans 4:25—“He died on account of our sins, and he rose on account of our justification”—Augustine argues that in Easter, “a certain passage (transitus) from death to life is marked off as holy in that passion and resurrection of the Lord” (Ep. 55.2; tr. Teske).

Despite Augustine’s own remark, however, in his preaching, he speaks of Christmas in more sacramental terms. This, in any case, is what Hubertus Drobner has argued in a lovely article on Augustine’s Christmastide homilies in Augustinian Studies. Drobner argues that Augustine not only treated Christmas as a sacrament but also drew on specifically the language of Nicaea: “only-begotten Son of God,” “begotten not made,” “born from the Father before all ages,” “Light from Light.”

But if Christmas is a sacrament—as Easter is—what kind of sacrament is it? What’s the mystery to which Christmas points?

Augustine views a sacrament, in Drobner’s language, as “a visible, terrestrial, and temporal item in the form of a thing (res), an event (factum, res gesta) or a word (verbum), which functions to transcend this world as a sign (signum, significatio) of the divine realm, which is invisible, spiritual, and eternal (a visibilius ad invisibilia, a corporalibus ad spiritalia, a temporalibus ad aeterna) (2004, 59).

Importantly, a sacrament involves us in the transitus it depicts. It doesn’t just communicate to us from a distance but draws us into God’s saving work.

For Augustine, the sacrament of Christmas is the “Mystery of Light.” It’s a time when we find in the in-breaking of light—the Eternal Day—in the darkest night of winter. It’s a sign of the invisible transition from darkness to light, both in the world and in ourselves.

Here’s Augustine himself, preaching at Christmas:

Even the day of his birth contains the mystery of his light. That, you see, is what the Apostle says: “The night is far advanced, while the day has drawn near; let us throw off the works of darkness and put on the armor of light; let us walk decently as in the day” (Rom. 13:12-13). Let us recognize the day and let us be the day. We were night, you see, when we were living as unbelievers. And this unbelief, which had covered the whole world as a kind of night, was to be diminished by the growth of faith. That is why, on the day we celebrate the birth of our Lord Jesus Christ, the night begins to be encroached upon, and the day to grow longer. (Sermon 190.1; tr. Hill)

In other Christmas sermons, Augustine describes the transitus from darkness to light like this:

• “This night, you see, is passing, the night in which we are living now, in which the lamps of the Scriptures are lit for us.” (Sermon 189.1; tr. Hill)

• “So, Christians, let us celebrate on this day, not his divine, but his human birth, by which he adapted himself to us, in order that by means of the invisible one we ourselves might pass over from visible things to invisible ones.” (Sermon 190.2; tr. Hill)

• “Let us pass beyond our fleshly condition. . . . Let us also pass beyond the condition of our souls. . . . Let us pass beyond all bodily, time-bound, changeable things.” (Sermon 369.2; tr. Hill)

There is more to Christmas than the story of Jesus born in Bethlehem, though that is of course wonderful, good, and true. Christmas is also a time to recall the extraordinary and paradoxical mystery that lies at the heart of the faith—that it is the Son of God, the unique, eternally begotten, only-begotten, begotten-not-made, born before all ages Son who was born of the Virgin’s womb in Bethlehem.

As the Church reflected more deeply on the mystery of the Incarnation, the implications were felt in the church’s liturgical participation in that mystery. The season of Christmas was surrounded by commemorations not only of the human but also of the divine birth of Christ. As a result, the birth of Christ in the Virgin’s womb 2000 years ago in Bethlehem was not only a commemorative event but a profound mystery that correlated with a full-throated affirmation that the Son was eternally begotten of the Father. Christmas was a sacramental mystery that invited the believer’s participation in the transitus from darkness to light.

In Christmas, as at Easter, we encounter a powerful transition from the visible, temporal, and material to the invisible, eternal, and immaterial. We are joined in the divine speech of the Word that draws us into the very mystery of God in Christ.

This essay was adapted from a longer essay at the Catechesis Institute website. Alex Fogleman is also the author of Making Disciples: Catechesis in History, Theology, and Practice.