Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law [1 John 3:4].

Again let me give you my very literal translation of this verse: “Everyone that doeth sin, doeth also lawlessness, and sin is lawlessness.” I have before me two very fine Greek commentaries, and they make it clear that the word translated “committeth” sin is literally “doeth” sin, meaning one who lives continually and habitually in sin. You know folk like that. I used to live that way, and the fellows working around me in the bank lived that way. Frankly, working in the bank was secondary. Our interest was in women, in liquor, and in having a good time. That was what we thought life was all about in those days, and that was what we called living. We lived in it continually, and we talked about it continually. That is what John means here: “Whosoever committeth sin”—whoever goes on committing sin, whoever simply lives in sin.
“Transgresseth also the law.” God has made certain laws. God did say, “Thou shalt not commit adultery” (Exod. 20:14), and He means that today also. All of this free, new way of looking at things is not a new way at all. It is as old as the hills. The fact of the matter is that it goes back to the jungle, it goes back to paganism.
“For sin is the transgression of the law.” God has put up the Law so that we can know that we are sinners, so that we can know what He requires. That is the purpose of the Law. The Law was never given to save, it was given to reveal to man that he is a sinner.
Sin is basically and fundamentally that which is contrary to the will of God. In other words, a sinner is one who is insubordinate to the will of God. A little girl was asked in Sunday school to give her definition of what sin is. She said, “I think it is anything that you like to do.” You know, she wasn’t far from the truth, because this old nature that you and I have is absolutely contrary to the will of God. Paul emphasizes that in Romans 8:5, “For they that are after the flesh [the old nature] do mind [obey] the things of the flesh; but they that are after the Spirit the things of the Spirit.” How are you living? In the flesh or in the Spirit?
Paul goes on to say, “For to be carnally minded is death …” Death is separation from God, and that is the thing which John is talking about. You cannot have fellowship with Him and be a carnal Christian. It is impossible to do that. I am afraid that there is too much talk today about, “Oh, how I love God, how I am serving Him, and How wonderful He is.” How pious some folk are! But, my friend, they are not in fellowship with Him because “… to be carnally minded is death; but to be spiritually minded is life and peace. Because the carnal mind is enmity against God [that is, disobedient to God]: for it is not subject to the law of God, neither indeed can be” (Rom. 8:6–7).
Paul makes it clear that before the Law was given there was sin, but it wasn’t transgression. The statement here in 1 John, “Whosoever committeth sin transgresseth also the law,” does not give a complete definition and is not really a good translation. That is why in my translation I have put it like this: “Everyone that doeth sin, doeth also lawlessness.” Paul wrote earlier in Romans, “… for where no law is, there is no transgression” (Rom. 4:15); but there is sin because he says, “Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned” (Rom. 5:12). That is, we sinned in Adam—his sin was ours. “For until the law sin was in the world: but sin is not imputed when there is no law” (Rom. 5:13). Man was still a sinner and was insubordinate to God; nevertheless, it was not transgression of the Law—because the Law hadn’t been given yet.
We read further in Romans: “Nevertheless death reigned from Adam to Moses, even over them that had not sinned after the similitude of Adam’s transgression, who is the figure of him that was to come” (Rom. 5:14). They sinned—why? Because they were sinners. In Isaiah 53:6 we have a true picture of every unsaved man: “All we like sheep have gone astray; we have turned every one to his own way; and the LORD hath laid on him the iniquity of us all.” Everyone has turned to his own way. Those three words tell our story: his own way. What’s your problem? What’s my problem? We want to have our way. The little baby in the crib is squealing at the top of his voice—what’s the matter with the little fellow? He wants his own way! We are born with that nature, a nature which is in rebellion against God.
This is the way the hymn “I Was a Wandering Sheep” by Horatius Bonar puts it:

I was a wandering sheep,
I did not love the fold,
I did not love my Shepherd’s voice,
I would not be controlled:

I was a wayward child,
I did not love my home,
I did not love my Father’s voice,
I loved afar to roam.

But the child of God has now come to God, and he has been born again.  McGee, J. V. (1991). Thru the Bible commentary: The Epistles (1 John) (electronic ed., Vol. 56, pp. 88–91). Nashville: Thomas Nelson.

3:4 commits sin. The verb, “commits,” in the Gr. conveys the idea of making sin a habitual practice. Although genuine Christians have a sin nature (1:8), and do commit and need to confess sin (1:9; 2:1), that is not the unbroken pattern of their lives. A genuinely born again believer has a built-in check or guard against habitual sinning due to a new nature (“born of God”—v. 9; Rom. 6:12). sin is lawlessness. The first reason why Christians cannot practice sin is because sin is incompatible with the law of God which they love (Ps. 119:34, 77, 97; Rom. 7:12, 22). The term “lawlessness” conveys more than transgressing God’s law. It conveys the ultimate sense of rebellion, i.e., living as if there was no law or ignoring what laws exist (James 4:17). MacArthur, J., Jr. (Ed.). (1997). The MacArthur Study Bible (electronic ed., p. 1968). Nashville, TN: Word Pub.