For he who lacks these things is shortsighted, even to blindness, and has forgotten that he was cleansed from his old sins."
2 Peter 1:22-23 (NKJV)
One time, as I was driving through a part of the United States, I saw a sign that indicated I could turn off of the main road to go to an area where there was a "scenic overlook". So, I did stop, but it was very hard to get a good view of the "scenic overlook" because some trees were blocking the view. After I moved around a bit, I was able to see the sight, but at first my view was obstructed, and until I avoided the trees that blocked my view, I was unable to really see the intended sight.
The Bible tells us about many things that God has done for us through Jesus, and how we can live the life that God has planned for us. In 2 Peter 1, Peter gives us a list of things we need in our life: faith, virtue, knowledge, self-control, perseverance, godliness, brotherly kindness, and love. Peter wrote that with these things we will never be unfruitful, and he also says that if we lack these things, we are short-sighted, even to the point of blindness, spiritually speaking.
Sometimes people have let things get into their life, and the view, the understanding, they should have of spiritual things has been obstructed. Things like bitterness, focusing on past sin and mistakes, unforgiveness, and even wrong doctrine can cause us to miss seeing the truth that God's Word shows us. We all need to make sure that we have an unobstructed view of the truth so that we can clearly see what God has done for us through Jesus, who we are in Christ, and how to do what God has called us to do.