James 4:17 - Sins of Omission.

Jam.4:17; Sins of Omission.

James 4:17 (NIV)  Anyone, then, who knows the good he ought to 
do and doesn't do it, sins.  

Like doing evil, failing to do good is also sin. [Ryrie SB]

We tend to think that 'doing' wrong is sin. But James tells us 
that sin is also 'not' doing right. (These two kinds of sin are 
sometimes called sins of commission and sins of omission.) It is a sin to 
lie; it can also be a sin to know the truth and not tell it. It is a 
sin to speak evil of someone; it is also a sin to avoid him or her 
when you know he or she needs your friendship. We should be willing 
to help as the Holy Spirit guides us. If God has directed you to do 
a kind act, to render a service, or to restore a relationship, do 
it. You will experience a renewed and refreshed vitality to your 
Christian faith. [Life Application SB] 

Omissions are sins which will be brought into judgment, as well 
as commissions. He that does not the good he knows should be done, 
as well as he who does the evil he knows should not be done, will 
be condemned. Oh that we were as careful not to omit prayer, and 
not to neglect to meditate and examine our consciences, as we are 
not to commit gross outward vices against light! [Matthew Henry 
Commentary]