This second letter by Peter speaks mainly about our knowledge of God, and that knowledge should prompt us to lead godly lives. He begins with, "His divine power has given us everything we need for life and godliness through our knowledge of him who called us by his own glory and goodness. Through these he has given us his very great and precious promises, so that through them you may participate in the divine nature and escape the corruption in the world caused by evil desires."
After speaking of knowledge, Peter then assures the people that they can know for a fact that the gospel is true. "We did not follow cleverly invented stories when we told you about the power and coming of our Lord Jesus Christ, but we were eyewitnesses of his majesty. For he received honor and glory from God the Father when the voice came to him from the Majestic Glory, saying, 'This is my Son, whom I love; with him I am well pleased.' We ourselves heard this voice that came from heaven when we were with him on the sacred mountain."
Did you catch that? Peter's saying, "We're not making this stuff up! We saw it with our own eyes!!!"
Peter, like so many of the other New Testament writers, also spends some time warning against false teachers. But again, notice that his definition of false teachers is those who are "denying the sovereign Lord who bought them."
Finally, Peter speaks of the second coming of the Lord. He reminds the people that "with the Lord a day is like a thousand years, and a thousand years are like a day. The Lord is not slow in keeping his promise, as some understand slowness. He is patient with you, not wanting anyone to perish, but everyone to come to repentance."
Have I mentioned that God keeps His promises? Always.