In a recent Stand to Reason podcast the question came up as to the irrationality of Christian faith.
A summary of the response by Greg Koukl:
Reason is grounded in the mind of God
If the scriptures are considered unreasonable, then you probably don't
understand them.
But the example of contradiction that is often brought up is the
Trinity.
Which law of reason does it violate?
It is said that it violates the law of non-contradiction: one god and three
gods.
And this clearly misunderstands the Trinity.
The scriptures do not hold out 'one god and three gods'. They show us one
God who subsists in three consciousnesses; integrated yet distinct, each sharing
the full nature of God in those separate consciousnesses.
A pale parallel is the family: one family with three members (mother,
father, child). A business partnership is similar: one partnership, say, three
partners, each severally and jointly liable for the obligations of the
partnership. But the great difference is that God the Father, Saviour and HS are all fully Yahweh! Neither of my illustrations achieve this level of ontological integration. Its as though the 'community' of the Trinity is akin to an imaginary number floating out of the number plane: all we can see is the number plane. We can know the imaginary number coming out of it, but can't quite grasp it...or at all!
Best illustrated in the triquetra, below.
The three vertices represent the three 'centres of consciousness' or persons; although, when we think persons we automatically think of spatially extended and differentiated beings. This is not so for God, except in the incarnate Son in his incarnateness - I think. And the hypostatic union itself is yet another mind-boggling item in scripture.
The arcs connecting the vertices represent the eternal and exhaustive communion of the three members of the Trinity in will, purpose and love. Each directly and reciprocally communing with the other two, permanently and as part of their being.