That which was from the beginning, that which we have heard, that which we have seen with our eyes, that which we saw, and our hands touched, concerning the Word of life
So the denial of this sinful nature is only to be self-deceived. And that is what John is referring to here, "If we say we have no sin (no sinful nature), we are deceiving ourselves." You see, the Bible teaches that basically I sin because I'm a sinner, and sinning doesn't make me a sinner, it only proves that I am a sinner. I have a sinful nature, therefore I sin. They liken it then to a horse thief. Stealing a horse does not make you a horse thief; it only proves that you are a horse thief. If you weren't a horse thief, you could never have stolen that horse. There's no way a man can steal a horse unless he is a horse thief. It's in your heart to do. You see, if it weren't in your heart to do, you couldn't do it. And so with sin, the sinful nature. So if I say or deny that, I'm just deceiving myself, and the truth isn't in me.Then, if we say that we have not sinned, I'm saying that this root of sin has born any fruit, then I make God a liar, because God has said, "All have sinned and come short of the glory of God." "There is none righteous, no not one. There is none that seeks after God." So God has declared that we are all sinners, and if I try to deny the fact my sinful root has never born any fruit, then I am denying the truth of God and making God a liar.