Benedicta sit sancta Trinitas atque indivisa Unitas: confitebimur ei, quia fecit nobiscum misericordiam suam. “Blessed be the Holy Trinity and undivided Unity: we will give glory to Him, because He hath shown His mercy to us.” (Introit, cf. Tobias 12:6)
The Feast: Wisdom Unveiled at the Threshold
Octave-day of Pentecost behind us, the Church pauses upon the first Sunday after the descent of the Paraclete to contemplate not a single mystery of the economy of salvation but its very Source and Term: the one God in three Persons. The placement is no accident of the calendar. Having traced the whole arc of revelation—the Father sending the Son, the Son returning to the Father, the Spirit poured out upon the Church—the faithful are now invited to lift their eyes above the works to the Worker, above the gifts to the Giver. As St. Gregory the Great observes, the soul that has received the Spirit is thereby fitted to gaze, however dimly, upon the Trinity whence the Spirit proceeds.
The feast is comparatively late in formal universal observance—John XXII extended it to the whole Latin Church in 1334—yet the worship of the Triune God is as ancient as the baptismal formula itself. The Mass is suffused with doxology, and its two principal readings frame the mystery from two directions: the Epistle in adoration of the divine incomprehensibility, the Gospel in the command to baptize into the divine Name.
The Epistle: O Altitudo — Romans 11:33–36
O altitudo divitiarum sapientiæ et scientiæ Dei: quam incomprehensibilia sunt judicia ejus, et investigabiles viæ ejus! “O the depth of the riches of the wisdom and of the knowledge of God! How incomprehensible are His judgments, and how unsearchable His ways!” (Rom. 11:33)
The Apostle, having labored through eleven chapters to set forth the mystery of God’s dealings with Jew and Gentile—the casting away and the ingrafting, the hardening that mercy might abound—does not conclude with a theorem but with a hymn. Reason, having gone as far as reason may, falls silent and adores. This is the proper movement of theology: not the abolition of the intellect but its consummation in worship.
St. John Chrysostom, commenting on this passage (Homiliæ in Epistolam ad Romanos, Hom. XIX), notes that St. Paul cries out O altitudo precisely where his own argument has reached its summit—as a man standing upon a great height who, looking down, is seized with awe at the depth below. The cry is not the confession of ignorance born of laziness but the reverence of one who has seen much and therefore knows how much more remains unseen. The judgments of God are incomprehensibilia, His ways investigabiles: not because there is anything irrational in God, but because the finite cannot encompass the Infinite.
St. Augustine returns again and again to this verse in De Trinitate, treating it as the very charter of the discipline. If we could comprehend, it would not be God we comprehended (si comprehendis, non est Deus). The depth of which Paul speaks is the depth of the divine essence itself, one and simple, yet possessed of riches—divitiæ—that the Latin theologians would later articulate as the processions and relations subsisting within the one nature. Augustine insists that the wisdom and knowledge here adored are not two things laid alongside the divine substance but are that substance: God does not have wisdom, He is Wisdom.
The Apostle then asks the unanswerable questions: Quis enim cognovit sensum Domini? Aut quis consiliarius ejus fuit? (“For who hath known the mind of the Lord? Or who hath been His counsellor?”—Rom. 11:34, echoing Isaias 40:13). No creature stood at the divine counsel; none advised the Uncreated. St. Ambrose, in De fide, presses this against the Arians: if no one was God’s counsellor, then the Son who is His Wisdom and the very consilium of the Father is not external to Him, not made, but eternally begotten of His substance. The verse that humbles the inquirer thus also confounds the heretic.
The doxology that crowns the Epistle is itself implicitly Trinitarian: Quoniam ex ipso, et per ipsum, et in ipso sunt omnia (“For of Him, and by Him, and in Him, are all things”—Rom. 11:36). The Fathers, and St. Thomas after them, were attentive to these prepositions. St. Thomas, gathering the patristic reading, sees in ex ipso the Father as fountainhead and principle, in per ipsum the Son through whom all things are made, in in ipso the Holy Ghost in whom all things are sustained and brought to their rest—the one operation of the undivided Three. Ipsi gloria in sæcula: to Him, the one God, be glory.
The Gospel: The Name and the Commission — Matthew 28:18–20
Data est mihi omnis potestas in cælo et in terra. “All power is given to me in heaven and in earth.” (Matt. 28:18)
If the Epistle ascends from the works of God to adoration of His incomprehensible essence, the Gospel descends from that essence into the world by way of the divine Name. The Risen Lord, upon the mountain in Galilee, speaks the words that have echoed over every font since: Euntes ergo docete omnes gentes, baptizantes eos in nomine Patris, et Filii, et Spiritus Sancti (“Going therefore, teach ye all nations: baptizing them in the name of the Father, and of the Son, and of the Holy Ghost”—Matt. 28:19).
The Fathers fastened upon the singular nomine—”name,” not “names.” St. Ambrose and St. Augustine alike draw the dogmatic conclusion: one name for three Persons, because one nature, one Godhead, one majesty. Were the three diverse in substance, Augustine argues, the Lord would have said in the names; the unity of the name confesses the unity of the essence, even as the distinction of the three confesses the distinction of the Persons. Here, then, is the Trinity not deduced by speculation but spoken by the Incarnate Word Himself, sealed into the foundational rite of the Church.
St. John Chrysostom (Homiliæ in Matthæum, Hom. XC) observes the order and the dignity of the commission. The Lord begins with His own authority—Data est mihi omnis potestas—not as one receiving a power He lacked in His divinity, but as the Incarnate Son to whom, in His assumed humanity, the Father has subjected all things. From this plenitude flows the mandate: first to teach, then to baptize, then to keep all that He commanded. Chrysostom notes that the same Christ who once restricted the Apostles to the lost sheep of Israel now flings the doors open to omnes gentes—the catholicity of the Church grounded in the universality of the divine power.
The Venerable Bede, in his homiliary, links the threefold structure of Christian initiation to the Trinity into whom one is baptized: we are made disciples by faith, regenerated by the laver, and perfected by obedience to the commandments—and the whole is enacted in nomine Patris, et Filii, et Spiritus Sancti, that the believer may be conformed to the very mystery he confesses. To be baptized into the Name is to be incorporated into the life of the Three.
And the Lord seals all with a promise that is itself a claim of divinity: Ecce ego vobiscum sum omnibus diebus, usque ad consummationem sæculi (“Behold I am with you all days, even to the consummation of the world”—Matt. 28:20). St. Augustine marvels that He who ascends into heaven does not thereby depart; the Ego sum who is with His Church to the end of the age is the same who was before Abraham, the Word who fills all things. Only God can promise an abiding presence unbounded by place or time.
Theological Synthesis: From Adoration to Mission
Set side by side, the two readings describe the whole movement of the Christian life within the Trinity. The Epistle is the exitus contemplated in reverse: all things are of, through, and in God, and the mind that perceives this is drawn upward into silent adoration of the depth it cannot sound. The Gospel is the reditus set in motion: out of that same fathomless God comes the command to gather the nations and to plunge them, by name, into the divine life.
The link between the two is the divine Name itself. In Romans, the Apostle confesses that he cannot comprehend the mind of the Lord; in Matthew, the Lord gives that very mind a name into which men may be reborn. What philosophy could only adore from afar, the Incarnate Word brings near in the Sacrament. The incomprehensibility of the Epistle does not contradict the intimacy of the Gospel—it grounds it. Precisely because God is the inexhaustible depth of riches, His self-gift in baptism is no impoverishment but an inexhaustible inheritance.
St. Thomas frames the matter with characteristic economy: the knowledge of the Trinity was necessary for us, he teaches in the Summa (I, q. 32, a. 1, ad 3), both for thinking rightly of creation—since God made all things not by necessity but by the love proceeding in the Spirit and the Word begotten of the Father—and for thinking rightly of salvation, accomplished through the Son Incarnate and the gift of the Holy Ghost. The two readings of this Mass are, in miniature, those two reasons: the Trinity as the principle of all things (Romans) and the Trinity as the principle of our redemption (Matthew).
Devotional Application
First, learn to end in adoration. Let the O altitudo of the Apostle govern your own pursuit of holy things. Study, read, inquire—but let the goal of every inquiry be worship, not mastery. When the mind reaches the edge of what it can grasp, do not turn back disappointed; kneel. The depth that exceeds you is not a wall but a sea, and you were made to be lost in it forever.
Second, live what was spoken over you at the font. You were baptized in nomine Patris, et Filii, et Spiritus Sancti. Renew that consciousness daily. Begin and end each day signing yourself with that Name, slowly and deliberately, remembering that the same words that made you a Christian are the summary of the whole Faith. Let the Sign of the Cross be a small confession of the Trinity, made with the whole body.
Third, take up the commission according to your state. Docete omnes gentes is the charge of the whole Church, fulfilled by each member in his measure—the priest at the altar and the font, the parent at the cradle, the friend in patient witness. To know the Trinity is never a private possession; the God who is eternal self-giving cannot be hoarded. Ask this Sunday whom you are called to teach, that they too might be baptized into the Name.
Closing Collect
Omnipotens sempiterne Deus, qui dedisti famulis tuis in confessione veræ fidei, æternæ Trinitatis gloriam agnoscere, et in potentia majestatis adorare Unitatem: quæsumus; ut ejusdem fidei firmitate, ab omnibus semper muniamur adversis. Per Dominum nostrum Jesum Christum Filium tuum, qui tecum vivit et regnat in unitate Spiritus Sancti Deus, per omnia sæcula sæculorum. Amen.
“Almighty and everlasting God, who hast granted Thy servants, in the confession of the true faith, to acknowledge the glory of the eternal Trinity, and in the power of Thy majesty to adore the Unity: we beseech Thee that, by steadfastness in the same faith, we may evermore be defended from all adversities. Through our Lord Jesus Christ, Thy Son, who liveth and reigneth with Thee in the unity of the Holy Ghost, God, world without end. Amen.”
Gloria Patri, et Filio, et Spiritui Sancto. Sicut erat in principio, et nunc, et semper, et in sæcula sæculorum. Amen.
A note on the citations: the patristic references above—Chrysostom’s homilies on Romans and Matthew, Augustine’s De Trinitate, Ambrose’s De fide, Bede’s homiliary, and the loci in St. Thomas—are reliable in substance and locus but should be verified against the Patrologia Latina/Græca or the Catena Aurea before direct quotation in publication, particularly the exact homily numbering, which varies across editions.
To go deeper: the Theology and Doctrine path treats the dogma of the Trinity through the Thomistic synthesis of processions, relations, and missions; the Sacred Liturgy path examines how the traditional Mass and Office are saturated with Trinitarian doxology, from the Gloria Patri to the Preface proper to this feast.