In 2 Peter, the threat to the church comes from within. False teachers were bringing false doctrine and immorality into the church. Peter wants to warn the saints away and strengthen them against such people who have risen among them.
How to do that? He starts off by saying the saints need to make extraordinary effort to grow spiritually, 2 Pet 1.5-11. Much needs to be added to faith for it to be effective and saving. Faith that just sits there doing nothing goes nowhere, certainly not to heaven. Neither will it be able to resist false teaching when it appears.
For such intense effort, how is one to keep from discouragement? By focusing on God and his power.
Perhaps Peter is remembering Jesus’ words, “This is impossible for mere humans, but not for God; all things are possible for God” Mk 10.27. (Matthew and Luke also include this saying, which must have struck a chord with all the disciples.)
So Peter begins his letter with a reference to God’s power and it is a theme in the letter, say some.
I can pray this because his divine power has bestowed on us everything necessary for life and godliness through the rich knowledge of the one who called us by his own glory and excellence, 2 Pet 1.3.
This truth is necessary to ponder, embrace, and practice before one can consider the enormity of the effort required to increase in faith.
When the power of God takes center place in our mind, the effort becomes a pleasure and a joy.
Let the work begin!