Sin begins with thoughts
The serpent first tried to convince Eve that God’s law was not the best for her, that the advantages of disobeying God outweighed the advantage of obeying him. The serpent’s deception was primarily directed against what Eve thought about God and his instructions (Genesis 3:1–6). Satan knew that once the mind was convinced, actions would soon follow.
Eve was persuaded by Satan’s lies and subsequently reached out to pluck the forbidden fruit. In the same way, the false teachers were Satan’s servants, deceiving the Corinthians to abandon their wholehearted devotion to Christ (see 11:14–15). Paul knew that thoughts are the primary battleground for spiritual warfare (see 10:5). That is why he took these false teachers so seriously. Paul equated the false teachers’ success with Satan’s victory in the spiritual war that was being waged in the Corinthian church.
Bruce B. Barton and Grant R. Osborne, 1 & 2 Corinthians, Life Application Bible Commentary (Wheaton, IL: Tyndale House, 1999), 429.