A gospel-centered doctrine of the Trinity

This post continues a series reviewing Daniel Migliore's book, Faith Seeking Understanding, An Introduction to Christian Theology. For other posts in this series, click a number: 1245.

"The Trinity" by Andrei Rublev, c. 1401
The task of Christian theology is to clarify an understanding of God that is appropriate to and fully congruent with the message of the gospel of Jesus Christ. According to Daniel Migliore in Faith Seeking Understanding, that is precisely what the historic doctrine of the Trinity accomplishes:
The doctrine of the Trinity...is the product of the meditation and reflection of the church on the gospel message over many centuries. In other words, the starting point or root of trinitarian faith is the good news of the love of God in Christ that continues to work in the world by the Holy Spirit. The doctrine of the Trinity is the church's effort to give coherent expression to this mystery of God's free grace announced in the gospel and experienced in Christian faith (p. 67).
Migliore expands on this thought by noting that the biblical basis for the doctrine of the Trinity, "is not to be found...in a few [Bible] proof texts" (p. 68). Rather, it is found in what he refers to as the "trinitarian pattern" of Holy Scripture - a pattern that is...
...Foreshadowed in the Old Testament according to the Christian reading of it, and found more explicitly in the witness of the New Testament to the presence of the one and only God in the saving work of Jesus Christ and the renewing activity of the Holy Spirit.
[Though] Scripture affirms from the beginning to end that there is but one God....the  New Testament [affirms that this oneness]...cannot be separated from God's love for the world in Jesus Christ and his renewing Spirit...
Christians call God triune because this way of speaking accords with the biblical witness and with the experience of the church rooted in this witness. Christians confess that there is one God (Eph. 4:6), who is none other than the Lord God of Israel and of all creation, even as they confess that "Jesus is Lord" (1 Cor. 12:3) and do so in the power of the Holy Spirit who is also acknowledged as the Lord (2 Cor. 3:17). The God known in Jesus Christ by the Holy Spirit is God over us, God for us, and God in us - the loving God, the gracious Lord Jesus Christ, and the communion-creating Spirit of God (2 Cor. 13:14). These are not three Gods but three distinct personal expressions of the one, eternally rich God who is love (1 John 4:8). The biblical narrative of God's reconciliation of the world through Jesus Christ and of God's bringing the work of salvation to completion by the power of the Holy Spirit implies a trinitarian understanding of God (2 Cor. 5:18-20; Rom. 5:1-5; Eph. 1:13-14). So, too, does the universal Christian experience of salvation, which as Catherine LaCugna notes, is "the experience of being saved by God through Christ in the power of the Holy Spirit" (pp. 68-69). 
Migliore urges us to embrace "trinitarian thinking" that stays aligned with the scriptural witness of the gospel. This will help us avoid "wild speculation" by leading us to use as our point of beginning and our continuing point of reference...
...The...economic Trinity (i.e., the one yet threefold agency of Father, Son and Spirit in the "economy" of salvation). All reference to the life of the...immanent Trinity (i.e., the eternal distinctions of persons within the being of God) rests on this basis. According to the gospel story, God is active as "Father," "Son," and "Holy Spirit" as the source, the medium, and the effective promise of liberating and reconciling love. To this beginning point in God's relationship to us through Christ in the Spirit trinitarian theology must return again and again. When Christians speak of God as eternally triune, they simply affirm that the love of God that is extended to the world in Jesus Christ by the Holy Spirit is proper to God's own eternal life in relationship (pp. 69-70).