Preaching the Mystery

This is the theological companion to the survey of Leo’s sermons: an account of what he preached. From the pulpit Leo proclaimed the Nativity as the elevation of human nature, summoning the baptized to “recognize your dignity” as partakers of the divine nature; he preached the Passion and Resurrection as the saving completion of that descent; and he set both within the admirabile commercium, the wondrous exchange by which God became man that man might share the life of God. The pulpit and the dogmatic Tome are shown to be one project — the same Christology spoken to the people and written for the council.

Tradition: Pan-Orthodox (Church Father / Latin)

The Mystery in the Pulpit

Leo’s preaching is best understood not as devotional commentary alongside his doctrine but as the pastoral form of his Christology. The same two-natures confession that the Tome states as proposition the sermons state as proclamation, addressed to a congregation and ordered to their salvation. What Leo preaches, feast by feast, is the single mystery of the Word made flesh — its descent at the Nativity, its consummation in the Passion and Resurrection, its fruit in the divinization of the redeemed — and he preaches it with the conviction that to grasp this mystery rightly is itself a saving act, since right faith in Christ is the condition of sharing his life (Sermon 21.2; trans. Feltoe, NPNF 2nd ser. 12). The doctrine is never abstract: it is always aimed at the hearer, who is told what Christ has done and therefore what he or she now is.

The Nativity and the Dignity of the Christian

The Nativity sermons (De Nativitate Domini, Sermon 21–30) are the brightest jewels of the corpus, and their governing theme is that the Incarnation does not lower God so much as it raises humanity. In the most famous passage of all, Leo turns from narrating the birth to addressing the baptized directly: “Christian, recognize your dignity, and, having been made a partaker of the divine nature, do not by unworthy conduct fall back into your former baseness” (Agnosce, o Christiane, dignitatem tuam — Sermon 21.3; trans. Feltoe, NPNF 2nd ser. 12). The logic is precise. Because the Son of God has taken our nature into union with his own, the human nature he assumed — and, through baptism, the Christian who is incorporated into him — is lifted to a dignity it could never have claimed of itself; the appeal to moral seriousness rests entirely on this prior ontological gift. The echo of 2 Peter 1:4 (“partakers of the divine nature”) is deliberate, and it shows Leo, in the Latin West and in plain catechetical speech, preaching what the Greek East would name theosis — the full development of which belongs to the soteriology of section 08 and to the wider Orthodox doctrine, but whose seed is here in the Christmas pulpit (Sermon 21.3; cf. 2 Peter 1:4).

The Nativity sermons are equally careful to guard the divine side of the mystery. Leo insists, again and again and often in balanced antithesis, that in being born of the Virgin the Word lost nothing of his Godhead: the assumption of flesh added a manhood without diminishing the divinity, so that the one born in time is the same who is eternally begotten of the Father (Sermon 22; Sermon 23; trans. Feltoe, NPNF 2nd ser. 12). The point is the heart of his anti-Eutychian and anti-Nestorian instinct alike: the natures are neither confused nor separated, and the single subject who acts is the one Christ, true God and true man.

The Passion and Easter

If the Nativity sermons preach the descent, the Passion sermons (De Passione Domini, Sermon 52–72) preach its purpose. This long Holy Week sequence is the largest single block in the corpus, and in it Leo expounds the Cross as the work of the whole Christ in both natures: it is as man that he suffers and dies, and as God that his suffering avails for the world, so that the two-natures confession is not a speculative nicety but the very condition of redemption — only one who is truly man can die, only one who is truly God can save (Sermon 54; Sermon 63; trans. Feltoe, NPNF 2nd ser. 12). The Passion sermons thus carry the doctrine of the Nativity sermons to its saving end: the nature assumed at Bethlehem is the nature offered at Calvary and glorified at Easter.

The Lenten Sermon on the Transfiguration (Sermon 51) stands as the hinge between the two. Preached in the Lenten course, it reads the light on Tabor as a disclosure, before the Passion, of the hidden glory of the one about to suffer — given, Leo says, to fortify the disciples’ faith against the scandal of the Cross and to show the whole body of the Church the glory promised to it in its Head (Sermon 51.3; trans. Feltoe, NPNF 2nd ser. 12). Here the preaching of the Passion and the preaching of the Christian’s exaltation meet: the glory shown on the mountain is the glory the redeemed are to share.

The Admirabile Commercium

Binding the whole of this preaching together is a single formula that Leo did as much as anyone to fix in the Western tradition: the admirabile commercium, the “wondrous exchange.” The idea is that in the Incarnation a saving transaction takes place — God takes what is ours, our humanity, that he may give us what is his, a share in his divine life; “the Creator of man became man,” in the words the Latin liturgy would draw from this tradition, “that we might be made partakers of his divinity” (theme of Sermon 21–30; cf. Sermon 21.3; trans. Feltoe, NPNF 2nd ser. 12). Leo states the same exchange in the compact maxim that Christ was born “to make us one with himself in manhood and to surpass us in Godhead,” and that he had to be both true God and true man — true man, to give us an example we could follow; true God, to bring a remedy no man could supply (Sermon 21; trans. Feltoe, NPNF 2nd ser. 12). This is the Western counterpart to the Eastern language of deification: the same soteriology of participation, expressed in the idiom of exchange rather than ascent. It belongs in the pulpit because it is good news — the announcement of what the hearer has been given — and Leo preaches it as such.

Pulpit and Tome as One Project

The decisive point, theologically, is that there is no gap between the Leo of the sermons and the Leo of the Tome. The famous formulations of the Tome to Flavian — that each nature does what is proper to it in communion with the other, that the Word and the flesh act in one person without confusion — are not innovations forced out by the Eutychian crisis but the precipitate of doctrine he had been preaching for years (Sermon 21–30 and 52–72; cf. the Tome of 449). The crisis gave the doctrine its conciliar occasion and its juridical form; the substance was already in the Christmas and Holy Week pulpit. To read the sermons after the Tome is to recognize the Tome’s sentences in their native homiletic setting; to read the Tome after the sermons is to see the pulpit’s proclamation hardened into the propositions a council could ratify. The pastoral and the dogmatic are, in Leo, a single enterprise — the one mystery of the two natures, preached to the people and confessed before the Church (Sermon 21.2; cf. the Tome). The further development of that Christology, and of the redemption it accomplishes, is carried forward in section 03 (the Tome) and section 08 (the theology of Christ and redemption); the sermons are where it is first heard.

References

Leo the Great, Tractatus septem et nonaginta (Sermons), ed. Antoine Chavasse, Corpus Christianorum Series Latina 138 and 138A (Turnhout: Brepols, 1973).
Leo the Great, Sermones, PL 54:137–468.
Leo the Great, Letters and Sermons, trans. Charles Lett Feltoe, Nicene and Post-Nicene Fathers, 2nd ser., vol. 12 (New York, 1895).
St. Leo the Great: Sermons, trans. Jane Patricia Freeland and Agnes Josephine Conway, Fathers of the Church 93 (Washington, DC: Catholic University of America Press, 1996).
The Holy Bible, 2 Peter 1:4.