2 Peter 1:8-9

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. But whoever does not have them is nearsighted and blind, forgetting that they have been cleansed from their past sins. 

they will keep you from being ineffective and unproductive 
John 15:1-2  "I am the true vine, and my Father is the gardener. He cuts off every branch in me that bears no fruit, while every branch that does bear fruit he prunes so that it will be even more fruitful."
Colossians 1:10  ... so that you may live a life worthy of the Lord and please him in every way: bearing fruit in every good work, growing in the knowledge of God, ...
Titus 3:14  Our people must learn to devote themselves to doing what is good, in order to provide for urgent needs and not live unproductive lives.

in your knowledge of our Lord Jesus Christ 
2 Peter 1:3  His divine power has given us everything we need for a godly life through our knowledge of him who called us by his own glory and goodness.

But whoever does not have them is nearsighted and blind 
1 John 2:11  But anyone who hates a brother or sister is in the darkness. They do not know where they are going, because the darkness has blinded them.

forgetting that they have been cleansed from their past sins 
Ephesians 5:25-27  Husbands, love your wives, just as Christ loved the church and gave himself up for her to make her holy, cleansing her by the washing with water through the word, and to present her to himself as a radiant church, without stain or wrinkle or any other blemish, but holy and blameless.
Matthew 1:21  "She will give birth to a son, and you are to give him the name Jesus, because he will save his people from their sins."

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