OT Background to the Doctrine of Trinity

“While the OT does not make explicit what is revealed by the coming of Christ and the writing of the NT, it does provide the essential foundation without which the full Christian doctrine of God could not exist. As [Gerald] O’Collins puts it, ‘The OT contains, in anticipation, categories used to express and elaborate the Trinity. To put this point negatively, a theology of the Trinity that ignores or plays down the OT can only be radically deficient,’ while from the positive angle, ‘the NT and post-NT Christian language for the tripersonal God flowed from the Jewish Scriptures,’ for though deeply modified in the light of Jesus’ life, death, and resurrection, naming God as Father, Son, and Spirit ‘found its roots in the OT.’ This is not to say that by the first century there had emerged in Israel a clear and coherent picture of plurality within the one being of God. This was clearly not the case. These ideas in the OT were scattered and had not formed into anything like a coherent picture. Notwithstanding, the OT provided the means both to distinguish and to hold together the roles of Son/Wisdom/Word and Spirit, since these were vivid personifications, not abstract principles. The ultimate acknowledgement by the church of the triunity of God was ‘providentially prepared’ by these foreshadowings. The OT personifications helped lay the groundwork for the eventual leap to persons, for ‘the post-exilic Jews had an idea of plurality within the Godhead’ and so ‘the idea of plurality within unity was already implicit in Jewish theology'” (Robert Letham, The Holy Trinity, 32).