One of the central mysteries of the Christian faith is the doctrine of the Trinity. According to it, there is but one God, yet that one God is threefold in nature: there is the Father, the Son, and the Holy Spirit. That God is triune in nature is a “mystery” in a special, theological sense of the term: it is communicated to humans by divine revelation, it is beyond the powers of natural human reason to demonstrate, and so if it is to be accepted, it must be accepted as an item of religious faith. Skeptics in their polite moments might call the doctrine a “mystery” in the more usual sense of the term. They will claim that the doctrine flouts elementary principles of counting, confusing one with three. For skeptics the only mystery to be explained is how Christians can think they remain faithful to monotheism while courting polytheism.