I think the foregoing is what some theologians have in mind when they say that we can only know God through Jesus. For we can only know God as Trinity if we start from revelation in Jesus. It does not follow, however, that we can know nothing at all about God apart from Christian revelation. It does not seem sensible for a Christian to doubt that Abraham and Moses knew much about God without knowing anything about Jesus. Many people think that there are good arguments for the existence of a good creator of the universe without any appeal to revelation at all. If God is revealed in Jesus, then God is revealed as Trinitarian. This does not exclude the possibility that God may be revealed in other ways or that it is reasonable to believe in God without any appeal to revelation.

What a Christian is entitled to say, then, is that God is truly revealed in Jesus as Trinitarian. But we do not fully comprehend exactly what this means. We are certainly not entitled to say that God is exactly as we understand God. We need to be rather less arrogant than that. The upshot is that we should never pretend to speak about the ‘inner life’, the ousia, of God as though we could make clear and correct inferences from Christian revelation to statements about what happens in the life of God apart from that revelation. What we can do is to say, ‘If God is revealed as Trinity through Jesus, then God must be such that this is a genuine revelation. It shows what God really is in relation to us and our understanding. But God may be infinitely more than that, and in ways we cannot at all understand’.

Does this mean that God is only Trinity in relation to us – to put it in traditional terms, that the Trinity is only a matter of the divine ‘economy’ (economia)?

I doubt if one should go as far as this – and that, perhaps, is Lacugna's problem of wanting both to say that we only know the economic Trinity and that God must surely exist in some way beyond human knowledge of God.