Peter wants to affirm the truth of the prophetic message (confirmed by the apostles), a message which the heretics have brought into doubt. To that end he makes it clear that the presence of the heretics is actually a confirmation of the prophetic message. Christian believers should understand that false teachers were predicted and confirm that the last days have arrived (see Matthew 24:4–5, Matthew 24:10, Matthew 24:23–26; Acts 2:17; Acts 20:29–30; 2 Timothy 3:1; Hebrews 1:2; James 5:3; Jude 1:18).1
3 knowing this first of all, that scoffers will come in the last days with scoffing, following their own sinful desires.