Fundamental Theology and Trinitarian Apologetics

I found Elias of Nisibis’s dialogue with the Vizier particularly interesting.  After working through the precise doctrine attached to the Christian understanding of God’s one substance and three hypostases, the vizier demands to know why, if Christians are truly monotheists, they confess that God is three hypostases.  This doctrine, as the Vizier sees it, is easily misrepresented and leaves Christians vulnerable to the charge of polytheism of which they are innocent. Elias replies with a question: why do Muslims speak of God as having hands, eyes, and the like? Certainly they do not hold that God has corporeal eyes or limbs; this interpretation merely confuses the hearers.

It is a question which proceeds immediately to questions of fundamental theology and epistemology. The Vizier has a response ready: these are the affirmations of the Qur’an, which must be understood in a non-literal way. Elias makes the same response: the Christian doctrine of the Trinity is affirmed by the Gospel, but it must be understood in a doctrinally nuanced manner.  This view of the question is properly ordered: the Trinity is known by faith, with rational accounts of it merely trying to render it comprehensible without displacing the scriptural foundation of the doctrine. In neither the Qur’an nor the Christian scriptures is the content of doctrine susceptible to proof merely on human rational terms.  

By taking the conflict to its ground in fundamental theology, however, does further conversation become impossible?  The Vizier affirms that “certain points that are debatable” which Muslims would contest still perdure. At what level does that debate occur?  Must it remain in the purely rational register of the preceding paragraphs, or does Elias’s argument open the way for an exchange and evaluation, on specifically scriptural terms, of Christian and Islamic doctrines of God?