The Bible
2nd Peter is written by Peter, one of Jesus’ closest followers. He is encouraging Christians to live a life consistent with the knowledge that God has saved them from sin. In the remainder of the book, he warns them about false teachers, just like Paul did in 2nd Timothy. Peter also assures them of the truth of the Bible, much like Paul did before. He lets them know he was an eyewitness to many of the things they have heard about Jesus and that the Bible came about through the Holy Spirit.
The people Peter is writing to are probably discouraged. Things are not going well for them, and they had been expecting Jesus would have returned by now. When people get discouraged, it is tempting to stop believing what God has told them. Peter’s solution is to keep living as God tells us and continue to believe what God has promised.