Peter begins his second letter with a challenge for his readers to confirm their calling in Christ. We do not save ourselves through any effort of our own. Our salvation is through the righteousness of Christ and is on an equal footing with the giants of church history such as Peter, and yet it does not hurt to be sure in our relationship—our election. After all, disciples who are active in the kingdom and in the ministry of Christ are doing their part to spread the kingdom to all.
The thing that Peter encourages his readers to do specifically, is to cultivate kingdom virtues in their lives. This is probably not an exhaustive list, but it does look as though Peter saw these virtues as building on each other, and building the disciples up into maturity.
To our faith (trust and obedience), which is the basis of our relationship with God and citizenship in the kingdom, Peter calls on us to add virtue (moral excellence, fulfilling purpose). Next comes knowledge. It is interesting that knowledge follows behavior on this list, as theoretical information hardly ever leads to anything useful. Temperance (self-control), perseverance (patience or endurance), and godliness (reverence or awe) follow. Once again it is clear that the Bible is calling not so much for people who store up vast quantities of information about its content, but rather people who understand enough to govern their behavior in ways that are beneficial to the kingdom.
The last two virtues could be translated into English with the same word: love. One is philidelphia, or brotherly love. and the other is agape, which is the sacrificial love exemplified by God. The pinnacle of Christian quality and character is not morality, judgment, or having everything “together”. It is love. If we allow ourselves to be governed by God’s Spirit and love, there is no law that can better steer our daily lives. Those who grow in these virtues can rest easy in the knowledge that their relationship is true.