• “If we say that we have no sin,” John is referring to what today we call Sin with a big ‘S’. This is what we call the sin nature within each person; it is a matter of the heart and desires. Paul put it like this in Romans 7:17: “But now, it is no longer I who do it, but sin that dwells in me.”
• “If we say that we have not sinned,” This is different; it refers to what we call sin with a little ‘s’. These are the sins we commit that come from the desires within us, or Sin with a big ‘S’. Here we are talking about thoughts, words, and actions. Paul also wrote about this in 1 Corinthians 15:3: “Christ died for our sins according to the Scriptures.”
It can be helpful to think of it this way: Sin is the disease, and sins are its symptoms. This time of year, I like to think about my garden and the weeds I need to deal with. I never plant seeds to get weeds; they are already there. If I don’t get the roots out, the weeds keep coming back. Sin, with a BIG S, is the root, and the weeds we see above ground are the sins, with a little s.