Ch. 1 --The apostle Peter makes it clear in this letter that he is reminding this congregation of believers of something they have already been taught. He has gone back through the character traits that set a child of God apart from everyone else in the previous verses, and warns them to diligently make their calling and election sure.
He doesn't tell them that they should judge each other with this list but themselves. Why? Because he knows that without these traits, they cannot stand against the attacks of Satan.
We who call ourselves Christians today would do well to study this list, go to the references given, and study those as well to make sure our election and calling is sure-- today more than any time in the history of mankind the congregation of God's children is under attack. Do we have what it will take to stand under it? In some cases do we have the knowledge of the living Word we need to know when we are even being attacked?
Peter says that if we don't have an intimate knowledge of the ways of God and how he works then we cannot expect to stand. He reminds them(and us as well) that it is not just his word, but the words of Christ himself and the other apostles who heard it the same as he did-- while they studied and learned from him for those three years. Vs. 20 says there is no private interpretation of the scripture, the reason for that was because the holy men of God spoke as they were moved by the Holy Ghost. They weren't just voicing their opinions as is the case so many times today.
May we be careful that we have a clear knowledge of the Word so that we may recognise false teachings when we hear it.