Audience: Christians (same audience as 1 Peter; see 2 Peter 3:1)
Subjects: Faith is ineffective without self-control and godliness, Interpreting scripture is not a matter of opinion, God is being patient with the world, etc.
Peter begins his letter by introducing himself and explaining that God has already given us everything we need to obey him, "godliness through the knowledge of him." (2 Peter 1:3)
Through God's promise of salvation through Jesus Christ, we are given the power to live according to the holy and divine nature of God, leaving behind our obedience to the world and its lusts.
Peter says we support our faith with (meaning our belief in Jesus Christ is supported by): self-control, godliness, love, endurance, and knowledge.
He explains that these things that support our faith allow us to not be "ineffective and unfruitful in the knowledge of our Lord Jesus Christ." (2 Peter 1:8)
Peter is plainly stating that knowledge of Jesus Christ and his sacrifice does not save people on its own. We must act on this knowledge, repenting of sin, showing fruits of a changed and obedient life, which is supported by the things he listed (self-control, godliness, etc.).
Peter says "For anyone who lacks these things is nearsighted and blind, and is forgetful of the cleansing of past sins." (2 Peter 1:9)
Paul too makes a statement about Jesus' sacrifice cleansing past sins in Romans 3:25. They are both saying essentially the same thing: Jesus' sacrifice cleanses us of our past sins, and we are expected to repent of sins as evidence of our acceptance of God's gift of salvation by living a godly and obedient life.
Peter says that if we have these things supporting our faith (godliness, self-control, love, etc.), then "entry into the eternal kingdom...will be richly provided for you." (2 Peter 1:11)
He explains that because this information is so important to salvation, he intends to continue to keep reminding them. Peter then explains that he was an eyewitness to all that occurred regarding Jesus Christ, probably as a statement of authority that he knows what he's talking about.
He knows what is necessary to be saved, and he is telling them that knowledge by itself is ineffective without the traits he listed supporting their faith.
All the authors of the New Testament make statements like this, such as James in James 2:17, "So faith by itself, if it has no works, is dead."
Peter then continues by saying prophecy is not a matter of each person's interpretation.
Having just said that prophecy is not based on personal interpretation, he immediately discusses false prophets/teachers (deceivers, antichrists) "who will secretly bring in destructive opinions." (2 Peter 2:1)
Peter is explaining that understanding prophecy and salvation is not a matter of opinion. Those who twist the gospel message of Jesus Christ will not be saved, but instead they will bring "destruction on themselves." (2 Peter 2:1)
Such people will use deceptive words for greed, teaching a gospel that only benefits them. Peter reiterates his point by saying that if even the angels who sinned and the ancient world were not spared (before the great flood), then neither will those who twist the message of God's salvation. Peter then returns to describing what such lawless deceivers are like.
Peter then makes a statement that is similar to Paul's explanation of obeying God in Romans 6:16. Peter says, "For people are slaves to whatever masters them," (2 Peter 2:19) either to righteousness or sin.
Peter explains that those who learn of God's salvation, yet return to disobeying God, it would be better for them to have never known. Jesus too talks about this kind of situation in Luke 12:47-48.
Peter reminds his audience that he has written to them before, regarding scripture and the teachings of Jesus Christ. He explains that while we are waiting for Jesus' return, there will be scoffers, but that we are to remember that God's words that created the entire world also predicted his salvation through Jesus Christ.
He also says, "With the Lord one day is like a thousand years, and a thousand years are like one day." (2 Peter 3:8) Peter explains that God is not being slow to fulfill his promise, but on the contrary he is being patient with us, because he wants everyone to repent and be saved.
Peter says, "You ought to live holy and godly lives as you look forward to the day of God..." (2 Peter 3:11-12 NIV) "Make every effort to be found spotless, blameless and at peace with him." (2 Peter 3:14 NIV)
Referring to Paul's letters, Peter says that Paul too speaks of these subjects, saying, "There are some things in them hard to understand, which the ignorant and unstable twist to their own destruction, as they do the other scriptures." (2 Peter 3:16) He continues by saying, "Beware that you are not carried away with the error of the lawless and lose your own stability." (2 Peter 3:17)
Peter is very clearly telling his audience to not sin or believe in a false gospel where sinning is allowed. As Paul says, "Do you not know that wrongdoers will not inherit the kingdom of God? Do not be deceived!" (1 Corinthians 6:9)
While the audience in 2 Peter is not plainly identified, because of Peter stating that this is the second letter he has written to this group in 2 Peter 3:1, it is very likely that his audience is the same as in 1 Peter.
Even though this letter is shorter than 1 Peter, he speaks of heavy topics explaining that: Faith is ineffective without self-control and godliness, Interpreting scripture is not a matter of opinion, God is being patient with the world, etc.