ISB ~ 1 Corinthians 5 v9

my letter:I.e., an earlier letter of Paul to the Corinthians that has not survived. Apparently the Church misunderstood his written instructions because the Corinthians assumed Paul wanted them to keep distant from all sinners without qualification. In fact, the apostle was suggesting they should isolate themselves, not from unbelievers in general, but from immoral Christians whose behavior was decidedly inconsistent with their beliefs. Tolerating their fellowship would only dishonor Christ and hamper their witness to the world.