Knowledge - after virtue, we are to add knowledge.

We will never know it all, we should always be willing to learn.

2 Peter 1: 

1 Simon Peter, a servant and an apostle of Jesus Christ, to them that have obtained like precious faith with us through the righteousness of God and our Saviour Jesus Christ:  

2 Grace and peace be multiplied unto you through the knowledge of God, and of Jesus our Lord,

3 According as his divine power hath given unto us all things that pertain unto life and godliness, through the knowledge of him that hath called us to glory and virtue:  

4 Whereby are given unto us exceeding great and precious promises:  that by these ye might be partakers of the divine nature, having escaped the corruption that is in the world through lust.  

5 And beside this, giving all diligence, add to your faith virtue;  and to virtue knowledge;