Second Peter focuses on two of Christianity’s basic challenges: First, is the gospel message reliable and second, is it unchangeable? Peter provides evidence for its trustworthiness, and warns against trying to change it to make it more palatable to worldly tastes.
In chapter one, three points stand out.
First, being a Christian requires spiritual growth. Sometimes, the christian “graces” (as the list in verses 5 – 7 are sometimes called) are not characteristics one adds to his life one at a time. All of these graces are to be characteristic of our lives all the time. Peter’s point here is that growth in these traits makes us effective and productive in our knowledge of God.
Second, the message Peter has preached about Jesus to his hearers is not something he made up. Rather, he was an eyewitness of the things he taught.
Third, Peter’s witness is confirmed by the message of the Old Testament, delivered by men of God who were guided by the Holy Spirit – God Himself. No one should ever doubt the message, call or seriousness of Christianity as the way of God.