The doctrine of sin is central to Christianity, since its basic message is about redemption in Christ. Christian hamartiology describes sin as an evil act of offence against God by despising his persons and Christian biblical law, and by injuring others. In Christian views it was an evil human act, which violates the rational nature of man as well as God's nature and his eternal law. According to the classical definition of St. Augustine of Hippo sin is "a word, deed, or desire in opposition to the eternal law of God."
–Wikipedia