1-2: Peter's self-given titles communicate his authority as apostle and humility as servant. He refers to a faith built on God's righteousness rather than our own.
3-7: God calls us to partake in His divine nature and escape from corruption. Because God granted us eternal life we should supplement our faith with virtue, knowledge, self-control, steadfastness, godliness, brotherly affection, and love. Each word builds off the previous, bringing clarity and instruction. Virtue (living a moral life) is impossible without knowledge (proper understanding of morality). Understanding morality is in vain if you don't have the self-control (willpower to avoid sinful desires). Self-control is just a temporary phase without steadfastness (perseverance in abstaining from sin). Steadfastness is misguided without godliness (living a life honoring to God) as our goal. Godliness requires showing affection towards our brothers. Brotherly affection is merely an empty action without love.
8-9: Productivity in our work for Jesus and knowledge of Him are stifled by sin. Increasing in these qualities will make us productive and fruitful. It also gives us assurance that we've been cleansed of our sins. Living in a rebellious way causes us to wonder if we've really repented and been forgiven.
10-11: Practicing these qualities keeps us from falling into sin and has a positive eternal impact as we enter the Lord's kingdom.
12-15: The qualities listed are worth memorizing because of the great benefit we gain from them. Peter knew he would die soon and give his readers a reminder so they could recall them when he was gone.
16-20: Peter, James and John witnessed Jesus being transfigured on the "holy mountain" where God spoke, confirming Jesus as his son and giving Him glory. This was confirmation for Peter that the prophecies about Jesus' 2nd coming were true.
21: This verse gives us insight into how scripture was inspired by God. While the authors wrote in their own words, they were guided and "carried along" by the Holy Spirit, writing exactly what God wanted to be written.
1-3: Just as there were true prophets there are also False prophets who secretly bring destructive heresies into the church. They're destructive because they lead people away from Jesus, the only hope of salvation. According to verses 2-3 their motive is money and sex. False prophets exploit people in the name of God, blasphemously causing His name to be associated with evil.
4-10: God can rescue the godly (those righteous through faith in Christ) from trials and temptations. Unrepentant false prophets will not escape judgment. Noah and Lot are given as examples of the godly being rescued while the wicked were being destroyed.
Some criticize the Bible for referring to Lot a "righteous man" after the evil things he did (offering his daughters for the men of Sodom to rape). If righteousness only meant that a person is sinless, they would have a point. However, the Bible is very clear that "all have sinned" (Romand 3:23) so we know it can't be saying lot never sinned. Whenever the Bible refers to a human as righteous, it always speaks of positional righteousness: their sins have been atoned for and they're righteous in God's sight. They no longer face judgement. Just as Abraham believed God and it was credited to him as righteousness (Galatians 3:6), Lot was only righteous in that God counted him righteous through faith.
11-12: Peter's indictment of the false prophets continues. Jude's list of transgressions closely matches Peter's. These teachers commit blasphemy for assuming God's role as judge and condemn Angels, who are far greater in might and power. Even Michael the archangel appealed to God's authority rather than his own when rebuking Satan (Jude 9). The wage for their wrongdoing is destruction on judgement day.
13-14: The deceptive teachers integrate themselves into Christian communities but are "blots and blemishes" who desire sin and entice people who have unsteady convictions. Their deceptions are revealed only after they've feasted and built trust with the community.
15-16: These false teachers are condemned for using God's name for financial gain the way Balaam did.
17: A waterless spring is the perfect analogy because they promise spiritual nourishment but lack substance. 'Mists driven by storm" are clouds that promise rain for crops but are blown away by the wind.
18-19: They entice people into sin, keeping them enslaved. They promise freedom but are themselves enslaved.
20-22: When an unrepentant person gains knowledge of their wickedness and forgiveness through Jesus, they may be convicted. They may even turn from certain sins but ultimately never trust in Jesus. If they choose sin and reject Christ after understanding the Gospel, they're worse off then before. With knowledge we're held to a higher level of accountability on judgement day.
1-2: Both of Peter's letters were reminders of prophecies and commandments his readers already knew through the teaching of the Apostles.
3-7: People scoff at the idea that Jesus will return to judge the world. Their rationale is that since we never see God intervene to judge anyone, God has never intervened and won't in the future. But Peter points out that God did intervene when he destroyed the world with water. He now waits for the day of judgement to destroy the earth with fire.
8-9: Although it's been thousands of years since God promised He would judge the world, it's a small increment of time from an eternal God's perspective. It's by God's grace that He has not destroyed the world yet. He is patiently giving us time to repent and trust in Jesus to avoid the wrath to come.
10-13: God will destroy the physical world and expose our evil works for judgement. Our desires, dreams, careers, health and material possessions will ultimately be destroyed. The focus of our lives should be serving God and growing in holiness for Him. Everything else is temporary and should be used for those ends. Those who have put their trust in Christ through repentance and faith wait for the new heavens and a new earth.
14-18: We should seek holiness in light of how temporary the physical world is, while seeing God's delay as an opportunity for the lost to be saved. Peter mentions Paul's similar statement in Romans 2:4 regarding God's patience and kindness leading us to repentance. Peter read Paul's circulating letters and acknowledged them as inspired Scripture. Ignorant, false teachers twist Paul's letters to fit their corrupt ideas. We must have discernment not to fall for their false teachings.