James 4:17 - Sins of Omission.

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

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]