1 Corinthians isn’t just a letter from a guy named Paul. It’s inspired scripture with deep and timeless lessons to teach us. It is widely understood to have been written by Paul during his three-year stay in Ephesus—around 55AD.
In 55AD, Corinth was a wildly successful cosmopolitan city, maybe too successful. Its problems seem to descend from its pagan, idolatrous lifestyle. Sexual immorality was widespread in Corinth, and that infected the church there. Paul wrote to them in order to correct this shameful behavior.
This is a classic problem with any church. Its members cannot help but be influenced by the culture they are marinated in. The church must strive to uphold God’s standards, or else the salt loses its saltiness.