1 Corinthians 5:1
It is reported commonly that there is fornication among you, and such fornication as is not so much as named among the Gentiles, that one should have his father’s wife. It is reported commonly that there is fornication among you, and such fornication as is not so much as named among the Gentiles, that one should have his father’s wife.
The church addressed stood in Corinth, a city notorious even among the heathen for gross immorality, and that setting reveals the moral climate in which the reported sexual sin occurred. That Corinthian corruption included prostitution tied to the worship of Venus and publicly supported by the city's religious and civic life. What was reported commonly was open fornication in the church, of a kind not even named among the Gentiles, that one should have his father's wife, the conduct of a believer violating even the low moral standard held by the Gentile world.
This sexual sin violates the seventh commandment and stands as a grave, knowing offense. Paul knew the state of the churches through what was reported commonly and declared to him by those who had the interest of the church at heart, and though absent in body but present in spirit he judged already concerning him that had done the deed. His first letter exposed this evil course and called the church to put away those evils before he visited, showing the church needed to act against those whose conduct disgraced it.
The verse means God's appointed minister must not fail to correct evils that exist and threaten the prosperity of the church, but must reprove them and deal firmly with them corresponding to their aggravated character, according to the light given of the purity, devotion, and piety to be maintained in the church. Applied to discipline, offenders should be suspended from church fellowship and the privileges of worship, rather than welcomed back on confession alone. Treating such sin lightly corrupts the young and brings God's displeasure upon the church. There is a time to speak and a time to keep silence, and faithfulness as a steward requires lifting the voice to stay evil and draw back the erring from evil.