There's is an excellent series of tweets on Ben Myers's twitter page concerning the doctrine of the Trinity. I thoroughly recommend it. A while back I started writing my own set of theses on the doctrine of Trinity, more as a rant than anything else. I quickly gave up, in part because that's how anything I begin to write usually ends, and in part because it was becoming clear that I'd be aligning myself with some form of heresy.
So, for example, thesis 1 was: "The doctrine of the Trinity is simply a way elaborating on the claim that Jesus is Lord," and, following on from this, thesis 2 was "The doctrine of the Trinity serves Christology, and not the other way around."
In a parallel universe, when historians of theology write the intellectual biography of the second best theologian to come out of Mervue, Galway in the early twenty-first century, they will call this my hyper-Barthian phase.
Anyway, the point is, the doctrine of the Trinity vexes me. It always has. And if Barth is responsible for the modern "turn to the Trinity," then I think it's one of his more regrettable gifts to the church. For it has given rise to all sorts of meaningless talk of perichoretic relationality, participation in the divine dance (or just participation full stop), divine mystery, and so on. Here my instincts are firmly with the early Melanchthon, who thought that such talk was for the worst form of scholasticism. Protestants, he argued, were interested in more concrete matters like law, sin, and grace - in short, the benefits of Christ given to an undeserving world. Melanchthon, it should be noted, later corrected himself, beginning subsequent editions of his theology handbook with a doctrine of God.
One of the fault lines in theology today is, essentially, whether to follow the early or the later Melanchthon. Barth, in typical fashion, disagreed with both the early and the later Melanchthon, though I'm sure he was entirely successful. Barth began (it seems to me) by trying to have the doctrine of the Trinity and Christology as equally basic. These, he claimed, where the distinctives of Christian theology. For my own part, I'm yet to be convinced that a doctrine of the Trinity per se is a Christian distinctive. What I mean is, I can imagine a Triune God who is quite other than the God revealed in Jesus. This is what the first two of my ill-advised theses were getting at. That is not to say that God is not Triune. But it is to say that God's Triunity, in abstraction from the concrete person of Christ, is an idol, perhaps even the worst of all idols.
Now you can see why I abandoned those theses.