It is one thing for Christians to maintain that there is only one God spoken of in the Bible. It is quite another thing to convince Christians that there are three persons in that one God. The capacity of theologians to persuade believers that two or three persons are really one God must rank as one of the great marvels of Christian history. We wonder how normally reasonably people can so readily accept what is ultimately declared to be an incomprehensible mystery. This is all the more remarkable when the Bible's own creedal statements never hint at any such terminology. There is no hint of a conundrum in the transparently simple affirmation that "there is one God, the Father."
- from pages 46-47, The Doctrine of the Trinity