“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.”  
2 Peter 1:8

“And beside this, giving all diligence, add to… godliness, brotherly kindness;” 2 Peter 1:5-7

Piety should not equate harsh judgmental expressions; one could be so ‘godly’; so pious that one begins to despise those deemed not as pious:
“The Pharisee stood and prayed thus with himself, God, I thank thee, that I am not as other men are, extortioners, unjust, adulterers, or even as this publican.”  Luke 18:11
So he says, add to godliness, brotherly kindness (Philadelphia- love of the brethren).
“Let brotherly love continue.”  Hebrews 13:1
“Look not every man on his own things, but every man also on the things of others.”  Philippians 2:4
“As we have therefore opportunity, let us do good unto all men, especially unto them who are of the household of faith.”  Galatians 6:10
This is something you should do; deliberately express love for the brethren, don’t despise those who are not where you are yet in terms of knowledge and use of faith:
“We then that are strong ought to bear the infirmities of the weak, and not to please ourselves.”  Romans 15:1
One sign of maturity is bearing the infirmities of those who are young and covering all of their faults in love.
Amazing that the word says, if you want to produce results in your life, be kind to others; love the brethren.
“Hereby perceive we the love of God, because he laid down his life for us: and we ought to lay down our lives for the brethren.”  1 John 3:16