"If it sounds as if I am suggesting that one has to be a genuine Christian or devout Jew to properly teach, preach, or write about the Bible, I am indeed suggesting that that should be the desideratum. If teaching is going to glorify God, edify the saints, and even educate, intrigue, and influence the lost, then, yes, that is what is most needed. It is true that some non-Christians can put Christians to shame with their biblical knowledge. If we are just talking about understanding biblical texts and ideas, it is indeed possible for a secular person to teach the Bible well at the level of information. But just as it is one thing to know the Bible, another to know the God of the Bible, it is also one thing to know the Bible and another thing to know the Bible is true, and God's Word.
"The Bible is not just intended for information and education. It’s not intended to be just a great piece of literature that merely intrigues or mildly inspires. It's intended for human transformation, and a teacher who cannot help an audience with the latter is handicapped. Indeed, a teacher who has not personally been transformed by the text cannot properly embody it, embrace it, model it, call for emulation of it, and the like. The Jewish or Christian teacher who is constantly coming to grips with the text will be constantly challenged to live it."
Ben Witherington III, Is There a Doctor in the House? An Insider's Story and Advice on Becoming a Biblical Scholar (Grand Rapids: Zondervan, 2011), 125.