The doctrine of the Trinity, contrasted with the triadic formulas and the triple structure of the biblical experience of God, is implicit rather than explicit in Scripture.
By “triple structure” of biblical experience we mean that in both the Old Testament and the New, God is experienced as going forth out of himself (from his “aseity”) in revelation and redemptive action, and also creating in human hearts a believing response to his revelatory and redemptive action.
We can experience this triple experience of God in the first reading. It speaks of God “in heaven above and on the earth beneath,” that is, of his aseity (he is Yhwh, God who is); of his transcendence (in heaven above); and of his immanence (on earth beneath). It speaks, too, of God going forth out of himself in his acts of revelation and redemption.
The first revelatory act of God specified is the original act of creation (“the day that God created man upon the earth”); the second is his speaking out of the fire in the giving of the Law on Mount Sinai. The redemptive act it speaks of is the Exodus, when God took a nation for himself by signs and wonders, which he did before the eyes of his people in Egypt.
This redemptive act, of course, provides the supreme type for his eschatological redemption in Christ, in which God brought into being a new people for himself by the “signs and wonders” of the Christ-event.
Finally, our passage speaks of the response that God creates in the hearts of his people—their faith in him who is, who reveals and redeems, and their obedience to his statutes and commandments.
Responsorial Psalm: 33: 4-5, 6, 9, 18-19, 20, 22
Today’s psalm highlights the Old Testament concept of the “word of the Lord,” which is one of several concepts that contributed to the Johannine conception of the Logos.
In the priestly narrative of creation (Gen 1), God brings the universe into existence by uttering his fiat: “Let there be light,” etc. It is to this action that the psalmist is referring when he says that God created the heavens through his word.
But with this formal affirmation the concept of the word is well on its way to becoming hypostatized, thus preparing the way for John 1:1 and forming part of the ingredients for the formulated doctrine of the Trinity.
When the letter to the Romans was read in course during the early summer of series A, these verses were skipped. They are eminently appropriate today, for they speak of God the Father (Abba); of the Christ, with whom we are co-heirs; and of the Spirit, who leads us as children of God. This supports our contention that the triadic formula is primarily a deposit of Christian experience.
The Christian believer knows that he/she has been adopted through Christ in baptism, and in the Eucharistic liturgy [he/she] is enabled by the Spirit to invoke the Father (for “Abba” is certainly a liturgical cry, derived from the ecstatic worship of the Aramaic-speaking Church).
Here, as in Galatians 4:6-7, Paul assumes that divine adoption is not a natural datum of human existence but an eschatological gift, made possible by the Christ-event and conveyed to believers through the operation of the Spirit (that is, word and sacrament).
In his controversies with the Corinthians, Paul had never denied the ecstatic gifts of the Spirit but always emphasized that the real test of the Spirit was not ecstasy but suffering in the way of the cross—hence the last point in this reading, the proviso that we must suffer with Christ now if we are to finally share his glory
This was the Gospel for Ascension Day in series A, where fuller comment can be found (See here). Here, of course, the emphasis rests upon the baptismal command, the clearest instance of the New Testament triadic formula that provided the basis for the later doctrine of the Trinity.
In the earliest Palestinian Church, baptism was administered in the name of Jesus (see Acts and Paul). The triple formula arose only toward the end of the first century, and then outside of Palestine (see the Didache).
Yet, from the earliest days baptism was understood to mean translation into the eschatological existence made possible by the Christ-event and participation in the gifts of the Spirit.
In a completely Jewish environment it would have gone without saying that if Jesus was the Messiah, he was the one in whom God had acted eschatologically, and if God had inaugurated the messianic age in Jesus Christ, this involved also the gift of the Spirit.
Thus, baptism was always implicitly Trinitarian.