St. John of the Cross in The Ascent of Mount Carmel (book II, chapter 6 to be precise) tells us that faith is the dark night of the intellect. It took me a great many readings to begin to understand what St. John meant by this statement. Faith accepts and integrates in a supernatural way what the intellect can only assent to.
For example, we know by faith that Jesus is fully human and fully God. We know this only by faith because, while the intellect may parse the sentence and be able to make a comprehensible statement of the individual words, the statement itself is not resolvable within the intellect. We can make all sorts of tortured analogies and metaphors, but the intellect "knows" that what is 100% one thing cannot be 100% something else. It is inconceivable that something might be 100% dog and 100% cat at the same time. So too, it is not possible to apprehend with mere intellectual prowess the means by which the truth is accomplished in Jesus. Nevertheless, we know it is. We know this by faith--the intellect assents to it, and thus seems to know it--but if we really grappled with the statement with mind alone we would not be able to resolve it. In the darkness of faith we assent and know this as part of the reality around us. It is truer than many things that we can prove, and more a part of our world. (For example how many people care about Euclid's hypothesis of parallel lines and points extraneous to them? How relevant is that for the majority of us.)
In the end, it is not what we know. We start by knowing, but eventually the understanding must be darkened because it is constantly looking for explanations and God will choose to perfect us in faith, where the understanding is rooted so deep that we have no need of proofs. The proofs are the breathing we do every day.
So, when wrassling with theological imponderables or Christological controversies, take heart. It little matters what the outcome, so long as the will continues to follow and seek out God, because our imperfect understandings will be perfected in the Dark Night of Faith.
(Yes, I know this is a horrific thought to the Jesuits and Domincans among us, but both St. Ignatius and St. Dominic eventually testify to its truthfulness. St. John of the Cross didn't come up with anything new, he simply stated it for all to see and read.)
I read through Ascent of Mt. Carmel and Dark Night of the Soul last Fall--wonderful! I was struck by St.John's wisdom, practical as well as mystical. I have learned and continue to learn a great deal from him.