Theologians on the interweb are having a jolly ding-dong about the at-first-glance-somewhat-obscure doctrine of the eternal subordination of the Son of God. Andrew Wilson has an excellent summary, with links to the various articles from the various combatants. The presenting issue is that some theologians are using the idea that the Son is eternally subordinate to the Father in support of a compelementarian view of gender relations: basically, if the Son is ontologically equal to the Father in every way, and yet submits to him eternally, that provides a pattern for equality-with-submission in the marriage relationship (and possibly elsewhere). But leaving aside the issue of gender, the deeper question is whether eternal subordination is an orthodox way of describing the relationship between the first and second person of the Godhead - and this question matters, because God is real.
In times like these, I do what I always do - reach for the Church Dogmatics. In this particular case, specifically IV/1, and the beginning of the chapter on The Obedience of the Son of God. So, how does Uncle Karl approach the question (which in his day was not so freighted with acute ethical questions)?
He begins by focussing, habitually, on Christ, and making clear that we are talking about the atonement that takes place in him and which is witnessed in both the Old and New Testaments. God's self-revelation in Christ is the source, ground, and content of our speaking here. We recognise from this source that the Son of God, Jesus Christ, is indeed God himself, the deity. There is no element of the NT which does not rest on this, and there is no element of the OT which is not caught up into it. But what is the significance of this attribution of deity to Christ? "The meaning of His deity... cannot be gathered from any notion of supreme, absolute, non-worldly being. It can be learned only from what took place in Christ" (177). In other words, we are relentlessly pushed back on revelation: no pre-conceived ideas of God - who he is, what he is like - can be allowed to qualify God's revelation in Christ. What it means for Christ to be God must be read off from the evidence of his incarnational revelation: "to put it more pointedly, the mirror in which it can be known (and is known) that He is God, and of the divine nature, is His becoming flesh and His existence in the flesh" (177).
But how are we to understand the obedience of the Son of God? "We cannot conceal that it is a difficult and even an elusive thing to speak of obedience which takes place in God Himself" (195). Barth briefly rejects Subordinationism proper (which gets around the problem by making the Son less than God, or at least not equally divine with the Father), and Modalism (which gets around the problem by making the obedience only an appearance of submission, "a kind of forecourt of the divine being" ). These solutions, often offered naively and harmlessly in the first few centuries of the church, must be rejected once their implications are seen, as they were rejected in the move to Nicene orthodoxy.
So Barth lays out three presuppositions to help move forward, "to engage (the difficulty) in frontal assault" (197). In brief, they are:
1. When we talk about the Son of God, we are talking about the subject and author of our salvation. "Anyone other or less than the true God is not a legitimate subject competent to act in this matter" (198) - therefore Subordinationism is ruled out.
2. The atonement is a genuine worldly event, which not only happens in the world "but affects it from within to convert it to God" (198) - therefore the entering into the world, the submission, of the Son of God is real and not only apparent, and Modalism is ruled out.
3. The atonement is a matter of the action of God being "identical with the existence of the humiliated and lowly obedient man Jesus of Nazareth" (199). Without in any way compromising his deity, God is in this man. "Everything depends on our accepting this presupposition, on our seeing and understanding what the New Testament witnesses obviously saw and understood, the proper being of the one true God in Jesus Christ the crucified" (199).
And so the conclusion: "Is it a fact that in relation to Jesus Christ we can speak of an obedience of the one true God Himself in his proper being? From the three inalienable presuppositions just expounded it is plain that we not only can do so but have to do so... We have not only not to deny but actually to affirm and understand as essential to the being of God the offensive fact that there is in God himself an above and a below... a superiority and a subordination" (200-1).
And of course that leads to the glorious (and polemical!) assertions about the servanthood of God in IV/2...
I think the central point for Barth, rightly, is the question of whether God is really revealed in Jesus Christ. If the relation of authority and obedience which we see in Jesus does not reflect anything in the internal life of God, then the incarnation is not revelatory but misleading; how could we then say that we know anything about God? However, if God really is revealed in Jesus, we cannot and must not allow any preconceived notions of what God 'must be like' to prevent us from accepting that revelation.