"Everyone who practices sin also practices lawlessness; and sin is lawlessness. You know that He appeared in order to take away sins; and in Him there is no sin." (1 John 3:4-5)What is sin? For most people, sin is like art, they cannot define it but they know it when they see it. As funny as that might be, the question as to what is sin is an important one given the place sin has played in the history of mankind. It was because of sin that man and woman were kicked out of the garden, it as because of sin that God destroyed the world with a flood, it was because of sin that death came to the human race, and it is because of sin that we still experience pain, loss, destruction, and death in our own lives and in the world around us. Finally, it is for sin that Jesus will once more return, bringing judgment with Him, to finish its destruction.
So what is sin? Most people define sin as some transgression of the law. For example, Adam and Eve sinned against God when they transgressed His command, "From any tree of the garden you may eat freely; but from the tree of the knowledge of good and evil you shall not eat, for in the day that you eat from it you will surely die." (Genesis 2:16-17) Such a definition is a legal definition of sin; sin as it relates to law. However, sin is more than mere transgression, it is a condition of the heart. Consider what Paul says regarding our salvation. "When you were dead in your transgressions and the uncircumcision of your flesh, He made you alive together with Him, having forgiven us all our transgressions, having canceled out the certificate of debt consisting of decrees against us, which was hostile to us; and He has taken it out of the way, having nailed it to the cross." (Colossians 2:13-14) Notice that we were doubly dead; dead in our transgressions and dead in the uncircumcision of our heart. Sin is more than the transgressions we commit, it is the condition of the heart out of which we commit those transgressions.
So what is sin? To best understand this, let's read the end of this verse according to Darby, "sin is lawlessness." Sin is when we chose our own way over God's way. Sin is when we refuse to submit to Him and His Word and chose rather to live by our own reason and will. It is as those in the parable that Jesus told who said, "We will not have this man to reign over us." (Luke 19:14 NKJV) Whenever we choose our own way over God's way we sin and when we live our lives on our own without regard to God we are sinners. This is what the prophet meant when he said, "All of us like sheep have gone astray, each of us has turned to his own way." (Isaiah 53:6) We are sinners because we have gone astray. We have followed our own way not God's way.
If sin were just transgressions, then there would be no need for Jesus to come to save us. Even under the Old Covenant there was provision for the forgiveness of sins. "All its fat he shall offer up in smoke on the altar as in the case of the fat of the sacrifice of peace offerings. Thus the priest shall make atonement for him in regard to his sin, and he will be forgiven." (Leviticus 4:26) However, while such scarifies could forgive sin, they could not remove sin from our heart. "For the Law, since it has only a shadow of the good things to come and not the very form of things, can never, by the same sacrifices which they offer continually year by year, make perfect those who draw near.. Every priest stands daily ministering and offering time after time the same sacrifices, which can never take away sins; but He, having offered one sacrifice for sins for all time," (Hebrews 10:1, 11-12)
Jesus came to remove sin from our lives, not just by forgiving us, but also by circumcising sin from our hearts. We are not just forgiven, we are cleansed and are no longer sinners by nature. This is what John meant when he said, "If we confess our sins, He is faithful and righteous to forgive us our sins and to cleanse us from all unrighteousness." (1 John 1:9) Not just forgiveness but cleansing also; cleansing us to live our lives for Him and for His Kingdom.