It's one of my favorite movies. And I'm not sure how leftist it really is. At the end, Hornbeck, the smarmy journalist, is revealed to be a lonely and petty figure because he doesn't believe in anything. Brady got lost "looking for God too high up and too far away"--he forgot the everyday miracles, and the greatest gift of all from God--free will and the ability to think for oneself. And Drummond was "just as religious as [Brady] was"; the difference being that he could reconcile Darwin and the Bible.
It was an anti-fundamentalist film, but I wouldn't go so far as to say that it was anti-Christian.