As I am studying through 2 Peter, I noticed how many times the word "knowledge" is used. Peter thought that it was important that knowledge grow in the believer. I think that is a big problem today that many believers simply settle for what the pastor tells them to believe and doesn't take the time to study or read the Bible for themselves. It is one of the reasons that many believers end up falling for so many false religions like Jehovah's Witnesses and groups like that today.
Wiersbe points out that Peter did not say that spiritual growth was automatic with the believer. Rather, in 2 Peter 1:10 he tells us "be all the more diligent to make certain about His calling and choosing you; for as long as you practice these things, you will never stumble." It is the believer and the Lord working together, the believer submitting his will to God that allows growth. The "these things" were mentioned in verses 5-7
"Now for this very reason also, applying all diligence, in your faith suppy moral excellence, and in your moral excellence, knowledge; and in your knowledge, self-control and in your self-control, perseverance, and in your perseverance, godliness; and in your godliness, brotherly kindness, and in your brotherly kindenss, love."
Peter goes on to say that if these things are growing in you, you will be fruitful and never useless when it comes to the kingdom of God. That is because, to the point where we reflect that we know Christ, then we are useful. To the point where I am surrendered and in his will and faithful then I am useful. To the point where I am still having my own way then I am not useful. Those parts of who I am still need to be pruned away.
This is not to say that knowledge always equates with spiritual maturity. Sometimes it leads to pride and legalism also. Those are two conditions we must watch out for. The Pharisees were blasted by Jesus because they were arrogant and thought they were self-righteousness. They pursued knowledge for knowledge sake and it became an end in itself. But, for the believer, it is never an end in itself. The pursuit of knowledge is so that I might grow in my relationship with God and know Him. He is the reason for this pursuit and to please Him.
I'm sure you have met people who are legalistic or self-righteous. Some churches seem to manufacture them like shoes. They are a poor example of what the faith is like because they do not see their need. When Moses or Peter came close to knowing God and into his presence, there were moments when they simply had to fall on their faces and acknowledge his holiness. Truth knowledge about God and who he is should result in this same type of humility. The more we know, I hope the more we want to know. But, the closer we get to the light, the more we realize our own darkness, our own need.
