“So then, if we do not do the good we know we should do, we are guilty of sin.” (James 4:17, Good News Translation)
You will not find a more simple, direct, or pure definition of sin than what is written in today’s scripture verse.
This definition does not cover all sin, but it does address what we refer to as “sins of omission”: Knowing but not doing. Following this principle, it might also be said that we sin when we have but do not share what we have with others.
James’ letter is, I think, the most practical book in the New Testament. It addresses the common issues of our life as disciples of Jesus, and is well worth the 15 minutes or so it would take a slow reader (like myself) to cover its five, short, chapters.
James reminds us that we need not sin. – Luther