Sin is a term used to describe a thought or action that violates some system of ethics, primarily in the religious context. Sin may be committed against either God (such as blasphemy) or against fellow man (such as murder). A list of sins, commonly known as The Seven Deadly Sins, include sloth, gluttony, pride, envy, lust, anger, and greed.
The confession prayer used in Anglican church services identifies three reasons for sin: ignorance, weakness and deliberate fault. That is to say, people sin either because they do not know that what they are doing is wrong; because they cannot help doing wrong despite their good intentions; or because they are malicious.
According to John, sin is the transgression of the Law. Some Christians see this as being the transgression of the "moral Law" as distinct from the "ceremonial Law" which they say were "nailed to the cross" (Colossians 2:14). (Other Christians don't acknowledge a differentiation between "moral" and "ceremonial" law.) Some theologians say in the Kingdom of God which is to come Christians will not sin, but this is stated by the Christians in the Reformation tradition as a purely legal definition which is imposed on us, forensically, by decree, from above, rather than the bottom-up objective sanctification of the soul which is the result of man freely cooperating with grace. In the former view, the New Covenant is seen as a global but staged process because sin is still present in Christians at this time. In the latter view, the New Covenant is a completed work by Christ on the cross, but is always "under construction" in its practical application to the individual Christian as we individually become refined like gold until all impurity is gone. At that point, we retain our free will and the possibility of committing sin, but we won't sin because it would go against our transformed nature.
Knowing what constitutes sin is important, since it enables us to avoid sins of ignorance and to guard against sins of weakness and deliberate fault. Various passages in the Bible act as a guide to what is sinful.
Jesus' teaching: The greatest commandments
When asked which were the greatest commandments in the Jewish law, Jesus answered:
Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind. This is the first and great commandment. And the second is like unto it, Thou shalt love thy neighbour as thyself. On these two commandments hang all the law and the prophets.— Matthew 22:37-40
This approach stresses the importance of a sincere heart and mind for avoiding sin. Sin is the result of insufficient love, so if we make sure that we love God and each other, we should not have to worry about sin.
St Paul's view: Faith
Before the time of Jesus, to sin was simply to break the Jewish law as set out in Leviticus and Deuteronomy. However, St Paul explains in his letter to the Galatians that, since Jesus' ministry and sacrifice, Christians should be guided by faith instead of the law (Galatians 3:25). He says "The acts of the sinful nature are obvious" (Galatians 5:19), implying that a person's own conscience should be sufficient to tell him or her what is sinful and what is not.
Paul goes on to list behaviour that he considers to be sinful: "sexual immorality, impurity and debauchery; idolatry and witchcraft; hatred, discord, jealousy, fits of rage, selfish ambition, dissensions, factions and envy; drunkenness, orgies, and the like." However, the context makes it clear that this list is not intended to be exhaustive, and other sins can be identified by the conscience of the individual.