I don’t read a lot of nonfiction, Christian or otherwise—apart from the Bible.
If we’re going to count the Bible, then my favourite author would be Luke, who wrote the gospel of Luke and the Book of Acts (I considered saying St. John, then remembered he’s also responsible for Revelation … so maybe not).
My Kindle says I’ve only read one nonfiction Christian book this year, Here by Lydia Sohn. I enjoyed it, but one book from an author isn’t really enough to make them a favourite.
(I have read more nonfiction than just one book so far this year, but the others were library books, and not Christian.)
I love Becca Syme’s books about writing (and not writing). Becca is a Christian, but her books are written for writers regardless of their faith so they don’t really count for this question either.
My other favourite possibly doesn’t count because he is a prolific and respected author and Bible teacher, I haven’t actually read any of his books yet (although I do have a couple on my to-read pile). I got to know him through his podcast, Ask N T Wright Anything, where NT (Tom) Wright grapples with listener questions about the issues of our time.
So my answer is John Mark Comer. In The Ruthless Elimination of Hurry and Practicing the Way, Comer encourages us to slow down and live the life God wants us to life. This means consciously avoiding the rush-rush-rush do-do-do that can lead to feeling disconnected from God, and slow down and connect.