Most of the Corinthians had been following Paul's instructions regarding women's head coverings so he commended them (v. 2), but he could not approve their practice at the Lord's Supper. They needed to make some major changes there. What they were doing cut at the heart of both the gospel and the church. This is the one certain situation in the Corinthian church that Paul addressed in chapters 7-16 that the Corinthians themselves had not asked him about. He wrote that he had heard about it (v. 18).
By way of background, we need to remember that in antiquity meals typically accompanied public worship in the early church, in Judaism, and in the pagan world. The early Christians observed the Lord's Supper as part of such a meal, often called the love feast.