Most evangelical presentations of the doctrine of Scripture are implicitly trinitarian. They identify the Father as Scripture's primary author, the Son as Scripture's central subject matter, and the Spirit as the immediate agent of prophetic and apostolic inspiration. Scripture is God the Father preaching God the Son by God the Spirit, to borrow J. I. Packer's famous description. Moreover, evangelicals recognize that the gospel of Jesus Christ, the central subject matter of Scripture, is implicitly trinitarian. The gospel concerns the love of God the Father for elect sinners, the suffering and glory of God the incarnate Son, and the fellowship of the saints in God the Spirit. The gospel is trinitarian in its root and fruit.
As salutary as this implicit trinitarianism is, there is more to be said about the relationship between the Trinity and Scripture. The Trinity is not simply the primary author of Holy Scripture and the organic structure of the gospel. The Trinity is the depth dimension of Holy Scripture, its principal subject matter and end. Matthew Bates's recent book, The Birth of the Trinity: Jesus, God, and the Spirit in New Testament and Early Christian Interpretation of the Old Testament, opens an illuminating window into to the trinitarian depth dimension of Holy Scripture.
Bates's book focuses upon early Christian "prosopological exegesis" of the Old Testament. Prosopological exegesis is a "person-centered reading strategy" that seeks to resolve the otherwise ambiguous identities of speakers and audiences in Old Testament texts in light of the clear determination of their identities in the apostolic gospel. As Bates demonstrates, both the New Testament and early Christian interpreters engaged in this sort of exegesis. For example, Mark 12.35-37 clarifies the identities of speaker and auditor in Psalm 110 as God the Father speaking to God the Son regarding his eternal generation and messianic dominion. And it clarifies for us that David overheard this conversation between the Father and the Son "in the Holy Spirit."
New Testament and early Christian prosopological exegesis overhears the story of "the conversational God" as it unfolds from its root in the Son's eternal generation and appointment as Messiah, through the Son's incarnate mission, death, and resurrection, to its ultimate triumph in the installment of the Son at the Father's right hand.
In Psalm 110.3-4, we overhear the Father say, "from the womb, before the dawn-bearing morning star appeared, I begot you," and we overhear the Father appoint this eternally begotten Son as messianic priest-king, "You are a priest forever after the order of Melchizedek" (compare with Psalm 2.6-9).
In Psalm 40.6-8, we overhear the Son speaking to the Father of the body he has prepared for him and of the Son's desire to do the Father's will in his incarnate mission (see also Heb 10.5-7).
In Psalm 22, we overhear the Son's cry of agony from the cross (vv. 1-2) and we overhear the Son praise the Father in the midst of an "ever-expanding" assembly of peoples after the Father has raised him from the dead (vv. 22-25).
In Psalm 45.6-7, we overhear the Son being addressed as the Father installs him on his eternal throne after he has obediently fulfilled the Father's commission, "Your throne, O God, is forever and ever. The scepter of your kingdom is a scepter of uprightness; you have loved righteousness and hated wickedness. Therefore God, your God, has anointed you with the oil of gladness above your companions" (see also Heb 1.8-9).
Such a reading strategy unveils the trinitarian depth dimension of Scripture in at least two ways. First, it reveals that Holy Scripture is not only God's Word to us; Holy Scripture is also witness to God's Word to God. How wonderful it is to read the Bible as a Spirit-inspired occasion to overhear God's intratrinitarian conversation! Second, this reading strategy helps us see that the great love story which unfolds in the pages of Scripture is not simply the story of God's love for elect sinners. It is the story of the Father's love for his eternal Son and of his desire to make him the head of a redeemed humanity, and it is the story of the Son's love for the Father and of his willingness to become incarnate and to endure suffering--to the point of death on a cross--out of zeal for the Father's glory among the nations (Ps 69.9; John 2.17). Prosopological exegesis helps us see that the story of God's love for us is but a modulation on the greater theme of the Father's love for the Son in the Spirit.
Prosopological exegesis is a person-centered reading strategy that helps us see the person-centered subject matter and the person-centered end of Scripture. It teaches us that the purpose of revelation, and of revelation's inscripturation, is to unveil God's intratrinitarian life of communication and communion and to welcome us into that life's embrace--at great cost to the triune God himself (Matt 11.25-27; 1 John 1.3-4). Holy Scripture is the product of the Holy Spirit, who enabled prophets and apostles to overhear the lovely words of the Father to the Son and of the Son to the Father, and who enables us to hear the testimony of the prophets and apostles in order that, through their testimony, we too may have fellowship with the Father through the Son in the Spirit.