What does 2 Corinthians 11:14 mean?

Paul has brutally called out his opponents in Corinth for what they were: deceivers pretending to be what Paul truly was: an apostle of Christ. They were attempting to seduce the Corinthians away from true devotion to Jesus, preaching to them a different gospel about a different Jesus and a different spirit. In other words, they were distorting all the true things Paul had taught to the Corinthians in order to gain some advantage for themselves.

Scripture indicates that this tactic should not be surprising. Satan also disguises himself as an angel of light. The Devil's greatest weapon has always been deception. The most effective deception is to convince people that what is evil is actually good, that what is dark is actually light. By coating lies in a veneer of truth, it's much easier to fool people into accepting what is false. Paul had already compared the work of these false apostles to Satan's deception of Eve in the garden (2 Corinthians 11:3; Genesis 3:1–8). He takes that even further in the following verse.