Some elements of Christian doctrine are like the catalytic converter of a car. Drivers know it's "in there somewhere" and the car probably couldn't function without it. But if ever asked to explain exactly what it is and how it works, they wouldn't know where to start.

J.I. Packer fears that many preachers have adopted this attitude concerning the Trinity, one of the most important tenets of the Christian faith. But the Trinity isn't a technicality; it's the central relationship of the Christian faith.

Packer is the Board of Governor's Professor of Theology (retired) at Regent College in Vancouver, B.C., author of Knowing God (IVP, 1973), and served on the editorial board of Christianity Today.

Packer is interviewed by Craig Brian Larson, pastor of Lake Shore Church in Chicago, Illinois, and co-general editor of The Art and Craft of Biblical Preaching (Zondervan, 2005).