"Knowledge makes for stability. Peter’s intention is to remind us of important points though we know and are established in the truth. That is, we are set fast, firmly fixed in the truth. Ignorant and unstable people will twist Scripture “to their own destruction.” We have been warned so we won’t be carried away with their errors and lose our own . The prophetic word we have is firmly fixed, sure and certain. It is something reliable enough that we can build on it. 

Peter writes with urgency because the Lord had made it clear to him that the end of his life was near. While he still has time, he will make every effort so that after his departure we may be able at any time to recall these things. (2 Pet. 1:15) He was willing to make every effort to remind us, but we still have to do our part. We can’t remember things we don’t know. Peter exhorts us to be all the more diligent to make our calling and election sure. We will never fall if we practice adding virtues to our faith. We have to pay attention and 'be diligent to be found by him without spot or blemish, and at peace' (2 Pet. 3:14). We must take care not to be carried away with the errors of lawless people."