Helen Waddell was a mediaeval scholar who also wrote historical novels, including one about the famous 11th-12th century philosopher/theologian Peter Abelard.  Toward the end of the novel two characters are discussing Abelard’s new theological work, De Trinitate (“On the Trinity”):

          ‘Have you read the De Trinitate, Gilles?  …And is it heretical?’

          ‘Of course it is heretical.  Every book ever written about the Trinity is heretical, barring the Athanasian Creed.  And even that only saves itself by contradicting everything it says as fast as it says it.’

Honestly, I think this is a very, very good thing.  The doctrine of the Trinity tries to avoid two alternatives:  God is NOT three separate entities, like the Three Musketeers.  God is also NOT one entity that wears three different masks, depending upon context.  Is there any middle ground after rejecting these choices? 

We must reject the image of the three-leaf clover (no matter what it might have accomplished for St Patrick in Ireland), we must reject the artistic image (so often depicted) of Christ on the cross, with the Holy Spirit as a dove flying overhead, all in the embrace of the old bearded Father.  We have to reject the language of “the Father sent His Son to die…” as though they were two completely different beings.  Is there a middle ground?  Not very likely, so it seems.  We insist (as Muslims and Jews do) on the one-ness of God, yet we include Jesus and the Holy Spirit in the package.  No wonder they regard us as polytheists!

So if we embrace the doctrine of the Trinity we must side-step rational thought processes that simply cannot grasp the concept.  This is OK—if you think for one minute that scientists have truly comprehended all the notions involved in quantum mechanics or the discoveries we are making about the nature of the universe, you need to be disabused in this area, as well.  “There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy” (Hamlet, I, v).

My suggestion is that any divinity we can totally comprehend is simply not God—it is at best a construct of our imagination, and at worst a ruse to mislead us.  I cannot (and therefore do not) try to “explain” the Trinity; I simply adore (love and serve) the Triune God.  Although the following words of St Thomas Aquinas were written with regard to the Real Presence in the Eucharist, they apply here, too:  Praestet fides supplementum/Sensuum defectui (“Faith stands ready as a helper/When the senses fail to see”). 

Don’t stress too much about “comprehension.”  Worry instead about devoted love.