Commentaries:
Paul was concerned that these people would be led astray, deceived by Satan, away from their spiritual purity. They would lose their spiritual chastity, as it were. They would begin fornicating, spiritually, with the world.
John W. Ritenbaugh
Satan (Part 2)
Paul had to deal with the Corinthian congregation because they had fallen under the sway of false apostles (see II Corinthians 11:13). These false ministers had convinced many of the brethren that they knew more and better than the apostle through whom they had heard, believed, learned, and been converted to the gospel. They were in the process of throwing aside what they had learned from Paul in favor of what they were hearing from these new "apostles."
John W. Ritenbaugh
Damnable Heresies