Faith and Reason was  not exactly a new idea in the Middle Ages. To combine Torah with Plato was already around from Philo. But to get the way they fit together was a Middle Ages invention. It was not to interpret the Bible as an allegory.

But faith with reason underwent a change because of Descartes's Mind-Body problem. Where is mind and reason valid? What do they measure. To get to the original synthesis of the Middle ages of Revelation with Reason you need to understand to extent and validity of reason.

How far can you trust spiritual experiences to tell you accurate data? Maybe a lot? Maybe not where it disagrees with Reason? But then where is the realm of Reason? 

To my way of thinking Kant and Hegel are helpful to answer these questions. Yet Hegel has been significantly mangled up by people wishing to use his rich wealth of ideas for their political purposes. And Kant is not so much behind that in terms of  misuse.

My opinion is that both the school of thought of Leonard Nelson based on Fries and Kant is helpful along with Hegel. I do not see them as much in conflict as is  thought.

With Fries you have faith-i.e. immediate non intuitive knowledge. That is knowledge not based on reason or senses for areas outside of "conditions of experience." But with Hegel you find that reason can get through the veil of perception by means of dialectic. So while reason is to some degree  a negative force limiting what you can know, it also makes progress towards the Absolute Spirit.