It is significant that the second person of the Trinity is called the Son. Our automatic translation of "Son" into "Jesus" is a mistake that excludes the witness of the Hebrew Scriptures.
The continuity between the writers of the Old and New Testaments is that the history of the nation Israel and the history of the man Jesus were central to their concerns i.e. their understanding of the reality of God was based on human experience in time. This means that Israel was unique among the nations, not simply because they wrote their history, the Romans also did that, but that they interrogated their history in order shed light on the relationship between the nature of the world and their own nature, to inform us of the troubles and delights of the flesh.
The writers of the Hebrew Scriptures used their experience of human suffering, the contingency of all things, the loss of temple and land and the apparent absence of God, to write extra-historical books like the book of Job, Ruth, Jonah that reflected the dilemmas of being human. Thus, they did not begin theological reflection, reflection about God, from philosophy or theory, they were informed instead of their experiences of being human and being a nation among the nations. The Church took over this reasoning when it wrote in the New Testament about the experience of the life and death of Jesus.
This approach to theology held theology to account. Theology could not be mere wishful thinking, it had to be grounded, it had to take into account human experience, especially the experience of failed religious systems that crumbled under the weight of human witness.
Religious notions come up against reality. The narrative of the human that we find in Scripture is a narrative of failure as Israel faced exile in Babylon after the fall of Jerusalem and the destruction of the temple.
Similarly, the New Testament has at its centre the tragedy of the crucifixion and death of Jesus and the apparent emptying of all hope and meaning. Christian theology does not emerge from a hopeful attitude or a triumphant religious sentiment. It emerges from a cry from the cross by one who we had hoped would be the Messiah, the anointed. This seditious cry: "My God, my God, why have you forsaking me?" marks the lowest point of human experience where darkness rules over all. If a kindly Father God was looking down from above ready to intervene for his Son he must have turned aside so as not to see.
Christian theology regards the life and death of Jesus as the objective basis for faith. As is apparent from the above, it took its cue from the Hebrew Scriptures. This beginning point is quite different from beginning with a notion of God derived from a perceived order in the universe or from philosophical speculation or, indeed, from a survey of world religions. The life and death of Jesus is the anchor in Christian theology that stops speech about God spinning off into self-serving speculation. While religion may be a story we spin to comfort ourselves, Christianity, has at its base an apparent failure, the scandalous death of the Messiah. It can never be understood and pursued as an antidote to our fear of death or meaninglessness. Rather, we are confronted by One who is "Other", One who speaks uncomfortable truths and who has no respect for our optimistic religious notions.
The Son in the Trinity denotes the historical experience of both Israel and the Church and is the starting point for all speech about God.
One would imagine that saying something about the Son would be easy. After all, Israel had a history and Jesus was an historical person. It would seem that we are on the safe ground of historical research and biography. This is far from the truth. Certainly, Israel had a history among the nations and Jesus was a man among men marked for death as are all men. But both Israel and the Church saw the character of God in the events that transpired.
Hence God is intimately connected with real events in the world, not as a being intervening in these events from the outside, as it were, but within the events themselves in the truth that they carried. Jesus comes to us in a form we least expect, he comes as a stranger and certainly not a creature of our own invention as we would expect if he were a made-up Messiah. The doctrine of the Trinity was the outcome of meditation on the relationship to these events in history, the truth that they carried and how that truth was present in all of time.
The narrative that the Church weaved in this respect became doctrine. For example, the event of the incarnation was not that a good man had been raised because of his righteousness to sit at the right hand of the Father but that the Father has sent the Eternal Word, the image of the Father Himself, to live among men and women.
This means that we must talk in the puzzling terms of the pre-existence of Jesus. This is a puzzle to anyone who sees only the man from Galilee. If we are to understand what the incarnation means we must deal with the idea of the two natures of Christ. Yes, he was a man who sweated in the midday sun and shared in the whole estate of humanity that included dying. However, the doctrine of the Trinity tells us more, that he was in the beginning with the Father as the prologue to John's gospel tells us. There was a truth about Jesus that went beyond his humanity so that he was the fulfilment of the character of God.
One difficulty that we have with the incarnation is that we work with Greek understandings of divinity. That God became man gets mixed up with Greek mythology in which the gods come to earth often to mate with human females. We automatically reject such a notion as ancient superstition.
Another difficulty, that is common to all theological understanding, is that we begin with only that which we know. We begin with a blank slate and a cynical attitude. However, the first step in understanding anything is to believe that it could be understood. This is the missing metaphysic of natural science. To proceed with science, we must have faith that the world is comprehensible. Theology is faith seeking understanding. We must chance our arm in believing, or even opening our rationality a chink, in order to even begin. Only then will we be able to understand what the Church means when it talks about things that seem to us impossible: that, for example, Christ was pre-existent, that God could become man.
Of the persons of the Trinity we must say that to see the Son is to see the Father and to experience the Spirit is to experience the Father. Thus, when we see the man Jesus destitute on the cross crying out in absolute dereliction, we see the Father. This means that all of our projections about God are forfeit in such a way that Paul may tell us that: "For Jews demand signs and Greeks desire wisdom, but we proclaim Christ crucified, a stumbling block to Jews and foolishness to Gentiles," (1Cor. 22,23) If Paul were a modern he could have included "modernity demands evidence".
The cross is foolishness to all our philosophical systems. Whilst the world can only see the destitute man, the Spirit reveals the image of God and the depth of truth about humanity.
As with the Spirit, there exists the danger of isolating the Son from the other two persons of the Trinity. Jesus becomes our own creature, our friend, confident and moral example and ceases to be the sign both of our judgment and our redemption. When any of the persons are separated from the other two, when Tritheism becomes a possibility, we know we are under the thrall of idolatry. We have seen the idolatry of the Spirit in enthusiast sects and we have seen the idolatry of the Son in the Jesus movement and in popular fundamentalism.
Any healing of the Church, which is now in disarray on all counts, must begin with a return to the conceptions of God produced by the early Church. Crucially, this involves the reintegration of the doctrine of the Trinity and the dispersal of the idolatry that has made the Church a laughing-stock. This alone is the answer to both the theism and the atheism that is, at present, destroying us.