No one can ultimately define God, not even as the Holy Trinity. The height of human arrogance is to suggest otherwise. All any of us can do is define not God, but our experience with God. There is a vast difference between those two things. The Trinity is a definition of our experience, nothing more. Those that make this definition of our experience the definition of God, and call it the "bedrock belief of Christianity" are not well informed.

The Trinity did not get defined until the fourth century of the Christian era. Paul and Mark are certainly not Trinitarians. In the debates of the third and fourth centuries that led to the Trinitarian formulation, only the Fourth Gospel was quoted to give the doctrine a biblical basis.

I have no trouble asserting that I experience God in Trinitarian categories, but to then assert that that the way I believe I experience God is the way God is, is a huge leap into idolatry. None of us can ever finally know who god is. So I will never say that God is a Trinity. That is to say more than I can know.

I will say that my experience of God is Trinitarian. That is, I experience God as that which is beyond all human categories, the Infinite Other. That is what Christians call the "Father and Almighty Creator." I experience God as Depth within, closer than my breath. That is what Christians call the Holy Spirit. Lastly, I experience God as a reality flowing through human lives and, for me, uniquely present in the life of Jesus. That is what Christians call 'The Son' and that affirmation is why I am a Christian. Since God by definition can only be one, I talk about my God experience as divine oneness in three manifestations. That is what the Church was trying to say with its doctrine of the Trinity. But all doctrines are attempts to describe the human God experience. They are not descriptions of God. That distinction is so often lost by clergy like the one you quote. People who assert doctrinal purity are normally asserting their authority as interpreters of ultimate truth. Someday they will learn, as we all must, that God does not need human defenders, and that all of us walk into the god that we believe that we have experienced.

-- John Shelby Spong