I'm reading it now for the first time (thanks for the link) so I really can't comment on the book, but when I was struggling with my own spiritual crisis my pastor taught me that faith isn't a feeling, nor is it a thing whose value we can discern through rational examination. It's a choice we are given. It's easy to love God when everything is going well. It's the times of uncertainty that put us to the test - not a "fail and you'll go to hell" kind of trial, but an opportunity to strengthen our souls. By placing our trust in God in spite of our doubt, we learn how to cross that temporal barrier and grow closer to Him. It is through this process that we transcend our ego and discover a treasure even greater than mortal satisfaction. We learn how to love Him not because of the rewards, but in spite of them. God doesn't say "I am that which I feel" or "I am that which I know", He says "I am that which I AM." Likewise, the mysterium fidei is not a veil we can pierce with our hearts or minds. We can only truly understand it's meaning by being faithful.

"Logic is the beginning of wisdom, not the end." - Leonard Nimoy