What does it mean that believers are a living epistle?
A living epistle means believers are themselves something people can read. Many will never pick up the Book and read it, but they can look at a believer and read. Therefore every believer must be careful what they practice, because believers and unbelievers alike are constantly watching and can read their lives.
Les teaches that Paul uses the phrase "living epistle" for every believer. Les explains that many people will never pick up the Book and read it, but they can look at a believer and read. Paul was trying to bring the Corinthians to understand that even though they lived amid abject immorality, idolatry, and mythology, wherever they went within that Greek culture they could be and were to be a living epistle—something the world around them could read and understand. This connects to Les's repeated point that grace is not license and that every believer must be careful what they do and practice, because believers and unbelievers alike are constantly watching. Not all things are expedient or edify, so the believer's conduct is a visible message.