Shared ground
Paul treats the situation as a real, publicly known scandal inside the Corinthian community (1 Corinthians 5:1–2). The act is described with broad language—sexual immorality—and then specified as a man “having” (living with) his father’s wife, implying an ongoing relationship. Paul frames this as shocking even by common non-Christian standards, which means he is not appealing only to insider rules.
Just as important, Paul’s main rebuke in these verses targets the community’s reaction. Instead of grief, they are “puffed up” (self-satisfied). Paul assumes that communal identity includes communal responsibility: the group’s posture toward known, serious wrongdoing says something about what the community values.
Where interpretation differs
Some debate focuses on what “his father’s wife” means. Many read it as a stepmother (the father’s wife, not the man’s own mother). Others think it could include the father’s current wife more generally. The passage itself does not spell out the exact family structure, but it does present the relationship as clearly out of bounds.
There is also some difference over how strongly Paul means “not even named among the nations.” Some take it as a literal claim about what outsiders would not tolerate; others read it as rhetorical emphasis—Paul stressing how far the Corinthians have drifted.
Why the disagreement exists
Paul uses short, socially loaded phrases rather than detailed description. “Father’s wife” is precise enough to indicate a prohibited relationship but not precise enough to settle every question about whether the father is alive, whether the woman is a stepmother, or how the relationship began. Likewise, comparisons to “the nations” can function either as an empirical observation or as a sharp contrast meant to shame.
What this passage clearly contributes
These verses contribute a clear moral and communal logic: (1) certain kinds of sexual conduct are incompatible with the community’s life together, (2) the community is accountable for its public stance toward serious wrongdoing within its own circle, and (3) pride in the face of such wrongdoing is portrayed as a fundamental mismatch with the seriousness of the situation. The specific action Paul expects (“removed from among you”) is introduced here as the fitting outcome of grief rather than arrogance, setting up the more detailed instructions that follow in the chapter.