The Catechism sections for today focus on the Trinity as the central mystery of faith. The Dogmatic Constitution, Dei Filius is the source of the supplementary material for today, expounding on the understanding of mysteries.

Paragraph 2. THE FATHER

I. "IN THE NAME OF THE FATHER AND OF THE SON AND OF THE HOLY SPIRIT"

232 Christians are baptized "in the name of the Father and of the Son and of the Holy Spirit"53 Before receiving the sacrament, they respond to a three-part question when asked to confess the Father, the Son and the Spirit: "I do." "The faith of all Christians rests on the Trinity."54

233 Christians are baptized in the name of the Father and of the Son and of the Holy Spirit: not in their names,55 for there is only one God, the almighty Father, his only Son and the Holy Spirit: the Most Holy Trinity.

234 The mystery of the Most Holy Trinity is the central mystery of Christian faith and life. It is the mystery of God in himself. It is therefore the source of all the other mysteries of faith, the light that enlightens them. It is the most fundamental and essential teaching in the "hierarchy of the truths of faith".56 The whole history of salvation is identical with the history of the way and the means by which the one true God, Father, Son and Holy Spirit, reveals himself to men "and reconciles and unites with himself those who turn away from sin".57

235 This paragraph expounds briefly (I) how the mystery of the Blessed Trinity was revealed, (II) how the Church has articulated the doctrine of the faith regarding this mystery, and (III) how, by the divine missions of the Son and the Holy Spirit, God the Father fulfills the "plan of his loving goodness" of creation, redemption and sanctification.

236 The Fathers of the Church distinguish between theology (theologia) and economy (oikonomia). "Theology" refers to the mystery of God's inmost life within the Blessed Trinity and "economy" to all the works by which God reveals himself and communicates his life. Through the oikonomia the theologia is revealed to us; but conversely, the theologia illuminates the whole oikonomia. God's works reveal who he is in himself; the mystery of his inmost being enlightens our understanding of all his works. So it is, analogously, among human persons. A person discloses himself in his actions, and the better we know a person, the better we understand his actions.

237 The Trinity is a mystery of faith in the strict sense, one of the "mysteries that are hidden in God, which can never be known unless they are revealed by God".58 To be sure, God has left traces of his Trinitarian being in his work of creation and in his Revelation throughout the Old Testament. But his inmost Being as Holy Trinity is a mystery that is inaccessible to reason alone or even to Israel's faith before the Incarnation of God's Son and the sending of the Holy Spirit.

IN BRIEF

261 The mystery of the Most Holy Trinity is the central mystery of the Christian faith and of Christian life. God alone can make it known to us by revealing himself as Father, Son and Holy Spirit.

The First Vatican Council Constitution, “De Fide Catholica” explains the mysteries of the Catholic faith in this way:

4. Now reason, does indeed when it seeks persistently, piously and soberly, achieve by God's gift some understanding, and that most profitable, of the mysteries, whether by analogy from what it knows naturally, or from the connection of these mysteries with one another and with the final end of humanity; but reason is never rendered capable of penetrating these mysteries in the way in which it penetrates those truths which form its proper object.

For the divine mysteries, by their very nature, so far surpass the created understanding that, even when a revelation has been given and accepted by faith, they remain covered by the veil of that same faith and wrapped, as it were, in a certain obscurity, as long as in this mortal life we are away from the Lord, for we walk by faith, and not by sight.

Footnotes

53 ⇒ Mt 28:19.
54 St. Caesarius of Arles, Sermo 9, Exp. symb.: CCL 103, 47.
55 Cf. Profession of faith of Pope Vigilius I (552): DS 415.
56 GCD 43.
57 GCD 47.
58 Dei Filius 4: DS 3015.