While Sanders' treatment is enriched by the theological reflection of the church, he is keen to underline that, "Trinitarianism is a gift of revelation before it is an achievement of the church." (p. 23). Biblical exegesis is therefore the key factor on constructing a doctrine of the Trinity. But this does not mean exegesis of individual texts in glorious isolation. Biblical revelation as a whole is Trinitarian in character. The Old Testament sets the scene for the missions of the Son and the Holy Spirit. The New Testament bears its witness to their coming into the world for our salvation. Individual texts need to be seen in that light. This overall approach has has the advantage of rescuing Trinitarian theology from the 'jigsaw puzzle' method.
Giving attention to the biblical materials, the author discusses 'New Covenant Attestation' to the Trinity, focusing on 'The Trinitarian Life of Jesus', 'Epiphany at the Jordan', 'The Threefold Name' and 'Paul and the Presupposition of Salvation'. He then discusses 'Old Covenant Adumbration'. Sanders is not happy to label manifestations of God in the Old Testament as 'christophanies'. Evangelicals have sometimes used that label on the basis that it is the Son's nature to be visible in a way that the Father is not, which is a contradiction of 'homoousios', that the Son has the same essence as the Father. Also, the idea that it was always the Son who put in a temporary appearance in Old Testament narratives deprives the eventual enfleshment of Jesus of its uniqueness. Better to say with Augustine that the theophanies represent, “simply the one and only God, that is the Trinity without any distinction of persons.” (p. 225). In the New Testament Isaiah's vision of the Lord seated upon the throne is predicated of both the Son (John 12:40-41) and the Father (Revelation 4:2, 8 cp. Isaiah 6:3).
That is not to say that we cannot glimpse distinct revelations of the three persons in the pages of the Old Testament. Sanders commends the Fathers' 'retrospective prosoponic (personal)' reading of Old Testament Scripture. The author cites the examples from the writings of of Gerhohus the Great (1093–1169),
Psalm 1: Wherefore: Glory be to the Father, Who knoweth the Way of the righteous; glory be to the Son, Who is the Way of the righteous, the Man Who is blessed, and prosperous in whatsoever He doeth; glory be to the Holy Ghost, Who is the Wind that scattereth the ungodly. As it was in the beginning, is now, and ever shall be: world without end. Amen. (p. 236).
Evangelicals have got themselves into something of a muddle on the doctrine of the Trinity of late. A narrowly biblicist approach has led to denials of eternal generation. Some have posited that the Son's will is eternally subordinate to that of the Father, attributing will to the persons of the Trinity rather than the divine nature. Sanders' approach provides a necessary corrective to these harmful tendencies. In an online article Adding Eternal Generation the theologian engages with Wayne Grudem's handling of the doctrine of the Trinity in the second edition of his Systematic Theology.
Evangelicals are by definition people of the Evangel. That is why we need to get the doctrine of the Trinity right. The revelation of the Trinity is umbilically joined to revelation of the mystery of the gospel. For in the gospel is nothing less than the good news that the Father has sent the Son to be the Saviour of the World and to raise up ruined humanity by the power of his Spirit. In the words of the Second London Baptist Confession, 1689 "which doctrine of the Trinity is the foundation of all our communion with God, and comfortable dependence on Him." (2:2). Sanders' study demands careful thought as he develops his argument and interacts with a range of other scholars, but the work is no way dryly academic. As he points out, to contemplate the Trinity is to seek the face of God and tune one's mind to doxology:
Glory be to God the Son,
Glory be to God the Spirit,
Glory, glory while eternal ages run.