The Trinity
In recognising God as our maker and ruler, we are thinking of a self. But one self in isolation is always incomplete. Some psychologists say that a child growing up without contact with other people could not develop a personality. Even if this is overstated, there seems to be enough truth in it to make me think that the description of God as one self in isolation must be incomplete.
"No man is an island, entire of itself; every man is a piece of the continent, a part of the main."
(John Dunn, Meditation 17 (1624).)
We need to resolve this defect in our understanding of God without denying his personality: he is more than a self, but not less. Nor must we appeal to created selves to fil the gap, as if God made us because he needed us. The only solution I can think of is that God is like a society. But what kind of society?
The only satisfactory answer I can see is the Trinity, one God consisting of three members united in purpose. I call them the Provider, the Mediator and the Indweller. In this divine society, as in a human family, the members are linked by relations of dependence.
The Provider, the fount of deity, is independent in every sense and as such remains separate from the world.
The Mediator has being because the Provider wishes it. The Provider interacts with the world only through him.
The Indweller has being because the Mediator (obeying the Provider) wishes it. The Mediator interacts with the world only in him. He is invisibly present in the world, responding to all that occurs, guiding the world towards its proper goal.
The Trinity's members are traditionally called the Father, the Son he "begot", and the Spirit, words taken from the New Covenant Book. "Father" and "Son" express unity of nature and purpose together with asymmetry of initiative and response, but fail to express the full scope of those members' functions, so I prefer Provider and Mediator. And I prefer Indweller over "Spirit". As regards the mode of the Mediator's dependency, traditionally called "begetting", I know not what word to use. One might broadly say "generation", but that traditionally refers to the Indweller's dependency, and I agree with tradition that the modes of the dependencies should be distinguished.
Spirit is the usual English rendering of the New Covenant Book's pneuma. It refers to invisible agency, such as wind, but especially to God preserving and renewing. These days "spirit" suggests a separate world, distant from everyday concerns, but I see no good alternative; ghost suggests something in a white sheet (originally scary, now often comical, always bizarre; hagia pneuma -- "God indwelling" -- used to be translated Holy Ghost), while wind and force fail to convey God's resemblance to a self. Selves are also said to have "spirit" in view of their destined union with God, in which they will be spirit.
I see this inner life of the Trinity as independent of the world, but maybe not independent of God's intention to create the world, for I think we can attribute creative intent to God's primordial nature. I therefore see no problem in my inability to describe the inner life of the Trinity "in itself"; I suspect that such a description would be vacuous. There is a circular description here but I hope not a vicious one.
"Creation is a belief Christians share with others. Should you not be seeking a broader agreement before moving on to a distinctively Christian belief like the Trinity?"
It is true that, historically, Trinitarian theory arose as a way of interpreting the intuition, experienced by Christ and by those who relied on him, that he was himself God, was also in relationship with God, and yet that Yahwism's belief that "God is one" was also true. But the theory is not logically dependent on the historic facts about Christ, so it would be possible to postulate it while unaware of them, though am not aware of anyone having done so, and do not claim to understand the mental process that would enable it. The matter is, in practice, untestable given the lack of ontologically-minded Yahwists ignorant of Christian tradition.
However, I think I can at least sketch how Trinitarian theory could arise independently. My theory has affinity with the one in Whitehead's Process and Reality (Part 5) and Hartshorne's The Divine Relativity. Adapting theirs, I postulate that God is absolute (initiating, masculine, yang, transcendent) and also relative (responsive, feminine [in relation to his own masculinity, not in relation to us], yin, immanent). However, those authors see God's two natures as mutually independent principles; more precisely, they see God's absolute nature giving way to relativity in the face of the independent realm of "eternal objects" or "pure potentials" (Whitehead's version of Plato's ideas), so that ultimate unity lies not in God but in impersonal "creativity". I reject that view. Instead I regard God as the only absolute, and the source of all diversity and relativity. But this seems too abrupt, there seems to be a missing link; I therefore postulate that God is not only absolute and relative but also mediatorial (outgoing, adventurous, unifying). I hope at some point to develop this formulation further, and that meanwhile it suffices to give some substance to my claim that in principle my theory is independent of Christian tradition.