The Christian "to-do" list
Peter lays out a roadmap of Christian maturity in these verses. All of the qualities and traits he mentions are after he mentions faith. Faith is the foundation upon which your Christian walk is built. Without faith, these qualities and characteristics do nothing for you. Practicing these qualities without faith may result in people calling you a "good person", but the practice holds no eternal value. We can't perform our way to Christ- it requires faith.
But faith is not the endpoint. Peter encourages us to add these things to our faith. And he says it will take effort on our part. Faith and the presence of the Holy Spirit inside of us gives us the power and strength necessary to grow to be like Christ. We play an active role in the growth process, though. We can't sit back and expect the Holy Spirit to magically transform us without us making daily choices to put into practice what God has revealed to us about His character. We do it in His strength, but we still have to do it!
Paul encourages us to "work out our salvation", and James tells us that "faith without works is dead". Then, there are the qualities themselves. All of these qualities are part of God's nature that we strive to emulate. The list culminates in love, marking our true destination and goal. God is love, so it makes sense that this would be the culminating step in the process of growing in Christ.
The traits are not one-time destinations that we achieve and then leave behind as we progress to the next. These are all traits that should be present in our daily lives. But I believe there is something to the order in which Peter presents them. We've said that faith is mentioned first because it is the foundation for everything. Love is mentioned last because it represents what God is, and therefore, our highest calling. So it makes sense that the characteristics in between are listed in some kind of order.
I believe they are listed in order of difficulty. Being good can be as simple as following the rules. Perseverance can mean to endure suffering and hardship while pressing onward. This seems more difficult to me than simply following the rules. Truly loving your neighbor, not just being courteous to them, can be harder than perseverance.
This progression of traits and an honest evaluation of yourself against each of the traits can give us some idea of where we are in our Christian walk. Again, though, the traits and growth in Christ are not tasks to be checked off the list and left behind. Our goal should be to practice all of these in our daily lives. If you don't always love your neighbor, give yourself a bit of a break. It's the hardest one on the list. If you can't practice basic goodness, though, try a little harder- it's the easiest one on the list.