1 Corinthians 5:9

I wrote unto you in an epistle not to company with fornicators (KJV)

Then: Members of the Church at Corinth received an earlier letter. This was the second time (at least) that Paul chastised them about keeping company with sexual immoralists. Obviously, he meant the assembled church. He didn't mean individuals should avoid talking with and helping transgressors hear the Lord's teachings, repent, and become followers or be restored to fellowship. The idea of "keeping company" needs split away from the meaning of "being in the presence of" and narrowed to "aligning oneself with anti-Christian values." Paul wants those who go into all the world to teach the gospel to stay personally pure and holy. He knows they cannot be effective if they accept pagan standards. The ultimate twist is the need for Paul to keep warning those already in the church. Trouble separating the line between secular and Christian behaviors and attitudes was an unfamiliar, complex muddle for these ordinarily competent sophisticates. Paul was not going to let them off the hook. He'd keep writing again and again.

Now: We have a two-pronged responsibility. The first is maintaining personal purity by reading, praying and keeping the knowledge of right standards ever before us. The second is to play the role of Paul in presenting Christ's standards to the world - through writing, through speaking, through living. None of us want to be like the Corinthians who tacitly (or actively) accept secular standards of sexualty, thus denying Christ who came not to change the law, but to fulfill it.