“In the church’s year, Trinity Sunday is the day when we stand back from the extraordinary sequence of events that we’ve been celebrating for the previous five months—Advent, Christmas, Epiphany, Lent, Good Friday, Easter, Ascension, Pentecost—and when we rub the sleep from our eyes and discover what the word ‘god’ might actually mean. These events function as a sequence of well-aimed hammer-blows which knock at the clay jars of the gods we want, the gods who reinforce our own pride or prejudice, until they fall away and reveal instead a very different god, a dangerous god, a subversive god, a god who comes to us like a blind beggar with wounds in his hands, a god who comes to us in wind and fire, in bread and wine, in flesh and blood: a god who says to us, ‘You did not choose me; I chose you.’
You see, the doctrine of the Trinity, properly understood, is as much a way of saying ‘we don’t know’ as of saying ‘we do know.’ To say that the true God is Three and One is to recognize that if there is a God then of course we shouldn’t expect him to fit neatly into our little categories. If he did, he wouldn’t be God at all, merely a god, a god we might perhaps have wanted. The Trinity is not something that the clever theologian comes up with as a result of hours spent in the theological laboratory, after which he or she can return to announce that they’ve got God worked out now, the analysis is complete, and here is God neatly laid out on a slab. The only time they laid God out on a slab he rose again three days afterwards.
On the contrary: the doctrine of the Trinity is, if you like, a signpost pointing ahead into the dark, saying: ‘Trust me; follow me; my love will keep you safe.’ Or, perhaps better, the doctrine of the Trinity is a signpost pointing into a light which gets brighter and brighter until we are dazzled and blinded, but which says: ‘Come, and I will make you children of light.’ The doctrine of the Trinity affirms the rightness, the propriety, of speaking intelligently that the true God must always transcend our grasp of him, even our most intelligent grasp of him.”
~ N.T. Wright, in For All God’s Worth: True Worship and the Calling of the Church (Grand Rapids: William B. Eerdmans Publishing Company, 1997), p. 24. http://www.amazon.com/For-All-Gods-Worth-Worship/dp/0802843190