“For if these things be in you, and abound, they make you that ye shall neither be barren nor unfruitful in the knowledge of our Lord Jesus Christ.”  
2Peter 1:8

In the preceding verses, he said:
“And beside this, giving all diligence, add to your faith virtue; and to virtue knowledge; And to knowledge temperance; and to temperance patience; and to patience godliness; And to godliness brotherly kindness; and to brotherly kindness charity.” 2 Peter 1:5-7
He goes ahead and tells us the results of lacking these things:
“But he that lacketh these things is blind, and cannot see afar off, and hath forgotten that he was purged from his old sins.”  2Peter 1:9
Notice he says, the one who lacks these things would be blind- spiritually blind, short sighted- lives for the present and still clueless about the word of God concerning the present, forgetful.
This is the reason why being a “church going only” Christian isn’t good enough but a massive recipe for disaster! These Christians are full of unbelief and exalt their physical observations above the word of God- this is because they have made no commitment to improve or invest in their knowledge of the word. They received the gospel by faith and remained there! The word of God says they would have trouble with certainty- certainty about their future, trouble with wisdom- wisdom on how to live in the present, trouble with sin- still thinking and giving leverage to their pasts.
This is not God’s plan for you, so he tells you, add moral excellence to your faith- think the right thoughts, add knowledge to that- be a student of the word, add temperance to that- after you have studied, live by the word, then he says, add patience to that:
“But let patience have her perfect work, that ye may be perfect and entire, wanting nothing.”  James 1:4
“And then as your endurance grows even stronger it will release perfection into every part of your being until there is nothing missing and nothing lacking.”  James 1:4, TPT