[Note: I am attempting to keep these SBD installments under 2000 words each, but that is--of course--quite inadequate for the topics covered. Consequently, these contributions are more programmatic than they are explanatory or defenses of the positions stated. You may access the whole series at my Serial page.]
The divine ontology is Being-in-Relation—the Christian narrative describes God as one and three.
Trinitarianism has a checkered history at the practical level. In the average congregation, or ministerial gathering, or seminary classroom, the subject of the Trinity comes as bad news rather than good. Just when we have struggled to believe in God, Christians also believe that God is, in some inexplicable way, both one and three. This incomprehensible affirmation seems to have nothing to do with daily life.
It is as if Christians come to know God first, and then tack on the Trinity as an addendum. Whether God is triune or not becomes insignificant to discipleship. When it appears that the God is better understood without the doctrine of the Trinity, some regard it as superfluous, though it may be reverently acknowledged as a mystery. When it seems incompatible with divine unity it is jettisoned by others.
But the confession of a Triune God is eminently practical and theologically rooted in God’s redemptive-historical self-revelation. Trinity is the Christian doctrine of God.
Economic Trinitarianism
We cannot begin with abstract ideas of threeness and oneness in discussing the Trinity. Instead, we begin with the concrete threeness of the Christian Scriptures. The starting point for Trinitarian thinking is the narrative of God where the Father, Son and Spirit participate in revelatory events (historical acts).
Christians did not begin talking about threeness because they were fond of the number. Rather, as they experienced God in Jesus through the Holy Spirit, they spoke in terms of three. The starting point for understanding the Trinity is the economic Trinity—God’s self-revelation in the narrated history of redemption. Jesus, the Son, prayed to the Father who poured out the Spirit upon him. This economic revelation is an authentic revelation of the God’s own identity (immanent Trinity, e.g., God’s own transcendent life before the creation). In the history of redemption, the one God is revealed as, in some sense, three.
The God of Israel is one God. There is no other. Israel confessed this monotheistic faith through the Shema: “Hear, O Israel, the Lord is our God, the Lord is one” (Deuteronomy 4:6). Paul unpacked the Shema where the Father is the one God and the Son is the one Lord (1 Corinthians 8:6). Christians reinterpreted the Shema as the affirmation of God’s community as well as unity.
The God of Israel sent the Son into the world—born of woman (enfleshed), born under the law (an Israelite)—who prayed to the Father as “Abba.” The Son who shares the reality of the Father as theos (God; John 1:1; Romans 9:6) became flesh and dwelt within the cosmos (John 1:14). As the monogenes theos (“the only God,” John 1:18), nestled in the bosom of the Father, he is the exegesis of the Father. The Son reveals the Father since he is one with the Father. The confessed identity of the Son—distinct in person but united as theos—moved Christians to worship the Son along with the Father (Revelation 5:13).
When Jesus, the Son of God, ascended to the right hand of the Father, the Father through the Son poured out the Holy Spirit upon Israel at Pentecost (Acts 2). By this Spirit believers cry out to the Father through the Son as “Abba” (Galatians 4:6; Romans 8:15-17). The Incarnate Son was the first Paraclete, the Spirit is the “other Paraclete” whom the Son promised he would send from the Father (John 14:16). The Spirit appears as the medium of the communion of Jesus with the Father and the means by which believers participate in Christ. This is clear in terms of the resurrection and the indwelling of the Spirit in Rom. 8:11-15. The Spirit is the one through whom we have fellowship with God—the Spirit is the presence of God among us since Jesus did not leave us as orphans (John 14:18).
The Christian experience of God is a communion with the Father, Son and Spirit. The presence of the Spirit is our communion with the Father through the Son (2 Corinthians 13:14; Ephesians 2:18, 22). Consequently, the very structure of salvation within Pauline texts (as an example) is triune (three-fold). Here are a few representative texts:
1 Corinthians 12:4-6: “the same Spirit…the same Lord…the same God.”
Ephesians 2:18: “for through him [Christ] we both have access in one Spirit to the Father.”
Ephesians 4:4-6: “one Spirit…one Lord…one God and Father of us all.”
2 Corinthians 1:21-22: “God who makes both us and you to stand firm in Christ…set his seal of ownership on us, and put his Spirit in our hearts.”
Galatians 4:4-6: “God sent his Son, born of a woman…because you are sons, God sent the Spirit of his Son into our hearts.”
Titus 3:4-6: “But when the kindness and love of God our Savior….He saved us through the washing of rebirth and renewal by the Holy Spirit whom he poured out on us generously through Jesus Christ our Savior.”
The three are one in their divine work to redeem humanity. The Father elects through the redemptive work of Christ as the Spirit renews God’s love in our hearts. This is a divine work from beginning (election) to end (transformation) which the Father accomplishes through his Son in the power of the Holy Spirit.
Johannine Trinitarianism
The Farewell Speech in the Gospel of John (chapters 14-16) depicts God as a three-fold (communal) unity. The four triune statements in the speech underscore the distinct personal identity of the Father, Son and Spirit but their shared communion in the unitary work of redemption and shared life (John 14:16-17; 14:26; 15:26; 16:7, 16).
The shared communion is characterized by love and mutual indwelling. This is quite explicit in the relationship between the Father and Son as each dwells in the other and they share a love for each other (John 14:10-11; 15:9; 17:21, 26). The Spirit represents and is the medium by whom the Father and Son continue their work in the redemptive story once the Son goes to the Father (John 16:28). As Jesus glorifies the Father and not himself, so the Spirit does not glorify himself but the Son (John 16:14). Precisely by not speaking of himself but bearing witness to Jesus, he shows himself to be the Spirit of truth. Distinct from the Father and the Son, he nevertheless belongs to both.
The Gospel of John pictures what some have called the “mystery of divine interpenetration” or “inness” (John 10:38; 14:10, 20; 17:21, 23). It represents an ineffable union, an intimacy transcending our finitude. Even though they are one, they are not one person. It is a unity in community—a communal oneness; it is organic and familial. The Father, Son and Spirit live in full transparency, love and mutuality.
The Triune God is the epitome of unity and diversity—united as theos they are also a community of love. They are the ground of the cosmos—God as Being-in-Relation. The cosmos is, at its root, both one and many, both one and three. Relationality is the cosmic ontology and this is rooted in the Christian doctrine of Trinity.
Iconic Trinitarianism
Andrei Rublev painted the “Holy Trinity” around 1411. He was beatified by the Russian Orthodox Church as “St. Andrei” solely for the extraordinary intensity and majesty of this icon. The image embodies the essence of Trinitarian dogma.
The icon portrays the visit of the angels to Abraham in Genesis 18 but excludes Abraham and Sarah from the picture in order to focus on the dogmatic meaning of the Trinity. The three sit around a table with a chalice as the centerpiece. The figure on the left—the Father—is arrayed in an indistinct gold (a transcendent tone), the figure in the middle—the Son—in brown (an earthy tone), and the figure on the right—the Holy Spirit—in green (the vibrancy of living earth). Each one is also dressed in blue to represent their equality—they are divine. The unity and diversity of the triune life is thus pictured in vivid colors.
Rublev depicts the theophany in an open circle with their heads gracefully inclined toward each other. The circular pattern embodies the theological idea of perichoresis—the loving dance of the Triune persons. Their faces are filled with peace and harmony while their gestures are gentle and loving. The Father and Son look at each other lovingly while the Spirit looks at the chalice as if to descend upon the cup. The chalice represents the Eucharist which is the center of Orthodox liturgy and its theology of redemption. The Eucharist is communion with the Triune God.
The open circle invites others to come to the table and experience the divine community. We are invited into the inner circle of God’s own life to sit at the table of God with God. This is salvation. As the ancient Orthodox sang (Lossky, The Meaning of Icons, 201):
“The blessed Abraham saw the Trinity,
as far as man can,
and regaled It as a good friend.”
So What?
Relationality—communal subsistence—is woven into the fabric of the cosmos itself. God is not an isolated, single monarch whose only relation is to rule. God is a community of equals (they share the divine nature) united in mutual love. The perichoretic love within the Trinity is a love willing to be vulnerable that sovereignly decides to enter into relationship with others. This is the heart of who God is as Creator and Redeemer. All forms of human love, then, are faint reflections of that Triune love internal to God’s own life.
The communion of the divine persons is a model for human community: family, church, and society. The doctrine of the Trinity provides the theological resources for communal life and relationality. We-in-the-plural images God (though it has been defaced by sin). This cautions against the individualism of modern culture as well as the individualistic soteriology of much modern theology (including Evangelicalism).
The doctrine of Trinity assures us of God’s economic presence through the incarnation and indwelling Spirit. God as Immanuel came in the flesh but now God dwells among us and within us as the Holy Spirit. The presence of the Spirit is the presence of God who links heaven and earth (2 Corinthians 13:14; Ephesians 2:18). The Father did not orphan us, that is, he has not left us without his personal presence. That presence is not mediated by some inferior being, angel or mediator but by his own Spirit in our hearts. God is still with us as the indwelling Spirit.
The triune picture of God grounds missionary theology. The divine community shares an intimate and full love for each other, but also extends that love in both creation and redemption beyond that community. In creation, the divine community shared its love with others. It invited those who are made in their image to participate in the joy of communion. In redemption, the divine community shared its love with a hostile and sinful humanity. The incarnation itself is the great missionary project and the model of all missionary activity. God himself came to a hostile world to invite it back into communion with the divine community. If the divine community is a model for the church and the church is to be one just as the Father and Son are one (John 17:20-21), then the church must ground its missional spirit in the doctrine of Trinity.
Liturgically, we praise the Father through the Son in the power of the Holy Spirit. This doxological approach keeps the economic roles of the Trinity in focus, preserving the fountainhead of the Father, recognizing the redemptive instrumentality of the Son and honoring the empowering presence of the Spirit. The Christological and pneumatological dimensions of Christian liturgy reflect the newness of God’s work in the present age. We do not worship God in the abstract but we worship the Father because he has acted in Jesus for our sakes and God is present among us by the Spirit. Liturgy, therefore, reflects the triune nature of God as the Father is praised through Jesus Christ in the power of the Holy Spirit.
Posted by John Mark Hicks 
