What Is Sin?
How did the Jews define "unrighteousness" or sin? How does society define sin? How would you define sin? How does God define sin?
Paul charged the Jews with knowing precisely what defines sin:
Dishonoring God (Romans 1:21)
Idol worship (Romans 1:23-25)
Sexual perversion (Romans 1:26-27)
Unrighteousness: evil, covetousness, malice, envy, murder, strife, deceit, maliciousness, gossip, slander, hate, insolence, haughtiness, boasting, disobedience, foolishness, faithlessness, heartlessness, and ruthlessness. (Romans 1:29-32)
The Jews knew that the Word of God included Laws:
"All who have sinned under the law will be judged by the law." Romans 2:12 (ESV)
Our society defines "sin" similarly, although it is not called "sin". We create laws to protect people from each other and to maintain social stability. Our human government is woefully inadequate and without integrity, but the definition of sin remains the same for our society as for that of the Jews: Fail to do what is right and you will be punished.
But that which is "right" or "wrong" changes with every people group and every generation. Working on a holy day was sin for the Jews, but not for our society. Homosexuality was once a sin for our society, but in this generation it is a celebrated privilege.
Our society, it seems, creates laws (defines sin) according to the amount of injury suffered or pleasure enjoyed, compared to one's lifetime. If an action causes harm to someone else, that action must be restricted. If an action brings pleasure to someone, it must be allowed. If an action causes harm to some, but pleasure for others, the action must be conditonally allowed. Few, if any, laws are created for future generations or for the society's ultimate good.
My own definition of sin emphasizes one's internal motivation for any action. "Sin" is a deeply held rebellion against God. We all have needs and wants, but "sin" is the human tendency towards satisfying those needs and wants without God. We feel lonely, and we desire to satisfy that need with another person, rather than communion with our Creator. We hunger for life, and we desire to satisfy that hunger with bread rather than God's Word. We are content to play in the mud of humanity than enjoy the excellent richness of Divinity.
How does God define sin?
"Both Jews and Greeks, are under sin, as it is written: None is righteous, no, not one; no one understands; no one seeks for God. All have turned aside; together they have become worthless; no one does good, not even one." Romans 3:9-12 (ESV)
SIN: hamartia (sin); from hamartano (to miss the mark and so not share in the prize; to err or sin); from meros (a division or share); from meiromai (to get as a section or allotment)
The essence of biblical sin is that of losing something valuable. "Sin", according to God, is any condition or action that results in the loss of something very good. "Sin" is that in a human which makes them ultimately worthless. This "sin condition" results in unrighteous behavior and rejection of God as one's Authority and Comforter.
"The fool says in his heart - There is no God. - They are corrupt, they do abominable deeds, there is none who does good. The Lord looks down from heaven on the children of man, to see if there are any who understand, who seek after God. They have all turned aside; together they have become corrupt; there is none who does good, not even one." Psalms 14:1-3 (ESV)
The essence of sin is the deeply held conviction that there is no Divine Authority over one's life: There is no God that Matters. The result of this core of rebellion is a life that progressively becomes corrupt, with increasingly abominable deeds.
What is sin?
Sin is a moral cancer.