"Whoever commits sin also commits lawlessness, and sin is lawlessness." (1 John 3:4 NKJV)
The following is from Bible.org:
The Doctrine of Sin
The word that is used most frequently is hamartia, missing the mark. It is the most comprehensive term for explaining sin. Paul used the verb hamartano when he wrote, “For all have sinned, and come short of the glory of God” (Romans 3:23). God has a high and holy standard of what is right, and so long as man follows the Divine standard he will see himself as he truly exists in God’s eyes. The flat statement of the Almighty is that all men have fallen far short of God’s required standard. It is the popular and common practice of men to create their own standards; however, God has established His standard of perfection for entry into Heaven, and all men have “missed the mark” as an archer’s arrow would fall to the ground because it fell short of its target.
Let no man ever think that he comes anywhere near the standard set by God. God has demanded absolute perfection, and no matter how one measures himself, he falls far short. Some men measure themselves on the basis of human intelligence, some by educational attainment, some by financial success, some by cultural environment, and others by religious performance. But God refuses to accept man on any of these grounds. He has established His perfect standard, and by that standard He measures every man. The Divine verdict in every instance has been the same, “You have come short, you have missed the mark.” And when the best of men have done their best, our Lord would challenge each with the words, “Which of you by taking thought can add one cubit unto his stature?” (Matthew 6:27). However much the difference that is lacking, no man can by himself raise himself to meet God’s moral standard, “For all have sinned, and come short of the glory of God” (Romans 3:23). Yes, all without exception, for, says God, “We have before proved both Jews and Gentiles, that they are all under sin” (Romans 3:9); that is, both Jew and Gentile have missed the mark.
Read more: http://bible.org/article/doctrine-sin