I think this is true of any expert. Anyone who has depth of knowledge in an area (I think of those tediously detailed discussions on Book TV or CSPAN) speaks about their chosen topic as if its history and issues are part of his personal past so that the players and events in those histories are more than facts in a mental catalog; they are memories with feelings and smells. Bob Sturm has assigned emotions to great sporting events in his lifetime as if he were personally invested in each. Phil Ligget can give details about every stage raced on the Alp d'Huez since 1965.
It inspires me when I come across someone with deep knowledge in an arena that holds my interest. John Kane knows more scripture by heart than anyone I know. He knows it by heart, not by rote, and when he recites it, he still registers emotion. He is identifying with it, taking it in, letting the word dwell in him richly. John Eldredge seems to speak out of a deep place about healing and warfare and intimacy with God. Thomas Merton never propped up a sentence in his life. His writing has always seemed to me to be eloquent without trying. He has known beauty in contemplation so when his pen is pressed to paper, beauty manifests in prose. I have a lot of respect for those men.
One of my fears is that I am not a spring but a vast and shallow sea - a pampas lake, a buffalo wallow. I like variety and I make brief sorties into new interests all the time. I like to meet new people and learn about their passions (if I can find anyone with any passion any more). And I can usually carry my end of the conversation - at least enough to properly interview them. But what is my passion? What subject have I studied so much, revisited so often, and meditated on so deeply that it reaches the core of my soul? What's yours?