"and to godliness, brotherly kindness; and to brotherly kindness, love." NIV translation
Next, we are to add godliness to our faith and this speaks to conforming our minds and actions to be like those of Christ. This is accomplished through the power and work of the Holy Spirit and is commonly called sanctification. The last two things that Peter tells us to work on are similar. The first is brotherly kindness which is talking about us demonstrating God's love to other believers. The last is love itself but here it is talking about us demonstrating God's love to the people that do not believe in Jesus.
"For if you possess these qualities in increasing measure, they will keep you from being ineffective and unproductive in your knowledge of our Lord Jesus Christ." NIV translation
Now, we see the reason that we are to work on these areas and that is so that we will produce fruit for the kingdom. This list of qualities will help us to produce quality fruit and an increasing measure will produce more fruit. That fruit is simply helping others to come to know Jesus Christ as their Lord and Savior. It is important to note here that Peter does not say anything here about our salvation but only our effective witness once we are saved.
"But if anyone does not have them, he is nearsighted and blind, and has forgotten that he has been cleansed from his past sins." NIV translation
If you are not growing in your faith and adding these things that Peter has listed, then your eyes are focused on the wrong thing. Many get caught up in the things of the world and spend more time on them than on learning about God or worship. They are focused on the here and now and have forgotten what it was like when they were first saved. This is what the believers in Ephesus were warned of in Revelation 2:4.
"Therefore, my brothers, be all the more eager to make your calling and election sure. For if you do these things, you will never fall, and you will receive a rich welcome into the eternal kingdom of our Lord and Savior Jesus Christ." NIV translation
Many have misunderstood Peter in this passage and took it to mean that we can lose our salvation but that is not what he is saying. He is saying that, if you grow in these things, you will be more sure in your heart and mind of what you have. You will not doubt and struggle with fear which is from the devil and you will receive your rewards in the second judgment. (Revelation 20)