Greetings Yankee,

"Whoever commits sin also commits lawlessness, and sin is lawlessness." 1 John 3:4 NKJV

Regarding this verse, The MacArthur Study Bible says:

"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 (1:18), 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)."

Dr. MacArthur has more on the passage, but if you have a MacArthur Study Bible you can look it up for yourself. If you don't have one, get one, it is an excellent source for exegesis of Scripture and has other valuable information.

In my opinion, Dr. MacArthur is an excellent Bible teacher, specializing in the epistles of John. I hope this helps.