What does 2 Peter 2:1 mean?
Peter ended the previous chapter by affirming the validity of the Old Testament prophecies about the Messiah. In no small part, Peter's confidence was based on his own personal experiences with Jesus. Peter now begins to warn his readers about false teachers.He acknowledges that false prophets have always plagued Israel, even in the days of the genuine prophets of God. Men would attempt to make a name for themselves, and mislead God's people by claiming that God had given them a message for Israel when He had not. Often, in fact, their false prophecies would directly contradict the messages of God's actual prophets.
Peter reveals that a similar problem was going to happen now for Christians. Rather than false prophets, it will be false teachers who will rise up amid the ranks of Christianity to mislead believers. What will they teach? Biblically, "heresy" is any teaching which contradicts or twists the truth. These doctrines are destructive to Christianity, attempting to internally change it to something false. They are also harmful to individual Christians, by leading them away from God's Word.
Peter warns that this won't be an obvious attack on the truth. These false teachers will try to introduce their deception secretly. Their goal, ultimately, is to convince Christians to join them in denying Jesus, the "Master" or "sovereign Lord." The following verses will reveal why anyone would do this. Regardless of motivation, the result will always be the same for those who attempt to mislead Christians into denying Jesus' place as Lord and Master: swift destruction.
In a modern application, we see groups even today which claim the title "Christian," but which deny the Lordship or deity of Jesus. They teach ideas contrary to the Scriptures, but claim them to be true. Some even deny that Peter's words and warnings in this book are the actual Word of God.