On the Holy Trinity Papeback -

Thedoctrine of the Divine Unity is a truth of natural religion; the doctrine of the Trinity is a truth of revealed religion. The various systems of natural theism present arguments for the Divine existence, unity, and attributes, but proceed no further. They do not assert and endeavor to demonstrate that the Supreme Being is three persons in one essence. It is because this doctrine is not discoverable by human reason, that the Christian church has been somewhat shy of attempts to construct it analytically; or even to defend it upon grounds of reason. The keen Dr. South expresses the common sentiment, when he remarks that "as he that denies this fundamental article of the Christian religion may lose his soul, so he that much strives to understand it may lose his wits." Yet all the truths of revelation, like those of natural religion, have in them the element of reason, and are capable of a rational defense. At the very least their self-consistence can be shown, and objections to them can be answered. And this is a rational process. For one of the surest characteristics of reason is, freedom from self contradiction, and consonance with acknowledged truths in other provinces of human inquiry and belief.