From the prologue we might have expected John to begin his "argument proper" with a discourse on the incarnation of Christ. But although his preamble begins with a strong assertion of the Incarnation, when he begins to interact with the teaching of antichrist, he begins at another place entirely. He begins with the moral issue.
This is the message which we have heard from Him and declare to you, that God is light and in Him is no darkness at all. If we say that we have fellowship with Him, and walk in darkness, we lie and do not practice the truth. But if we walk in the light as He is in the light, we have fellowship with one another, and the blood of Jesus Christ His Son cleanses us from all sin. If we say that we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness. If we say that we have not sinned, we make Him a liar, and His word is not in us. My little children, these things I write to you, so that you may not sin. And if anyone sins, we have an Advocate with the Father, Jesus Christ the righteous. And He Himself is the propitiation for our sins, and not for ours only but also for the whole world (1 John 1:5-2:2).
The source of our ethical stand is not an abstract list of rules, but rather the character and nature of God, the God who is light. And we see here one of John’s favorite types of expressions, which is to use a contrary statement for purposes of emphasis—"in Him is no darkness at all." We begin our argument with the holiness and righteousness of God.
Wanting to drive the point home, John repeats a particular pattern here three times. The form is something like this: "If we say that good is evil, we are liars. But if we know that only God is good . . ." John works through this pattern three times. The first is found in vv. 6-7, the second is found in vv. 8-9, and the third is found in vv. 10-2:1.
First is the false teaching—in each case, the error is introduced with the phrase if we say.
Then comes the contradiction—the error is denied by an expression such as we lie. The conclusion is found in the antithetical contrast—John goes on to state an important truth concerning the general matter. But if we walk . . .
John is fighting an evil "sinlessness." Remember the heresy of the Gnostics which John is concerned to refute, and pay particular attention to how the error advances, and how the truth answers error accordingly. The first error is that of saying that walking in darkness does not threaten a man’s fellowship with God. Those who assert this lie do not practice the truth. But if we walk in the light, we have fellowship with each other and the blood of Jesus cleanses us (continuously) from all sin. The second error is that of a man who says he has no sinful principle within him. This is the error of the Pelagian—the one who denies original sin. Such a man does not know himself, and consequently is described as self-deceived. This is a gross error but note the description of it. This man is lying, but the emphasis is on how he lies to himself. But if a man confesses his sins, the God who is without sin will forgive and cleanse. The third error is that of saying that one has done no sinning. Here the problem concerns a man’s testimony concerning his own actions. The Bible says that we all stumble, and that in many ways. If we contradict that testimony, then we call God a liar. But John’s point of writing this down is so that we would learn to not sin.
Later on in the epistle John will make some strong statements about the one born of God being incapable of sin. Those statements will be considered in their place, but every reader of the letter must recognize that John plainly acknowledges the fact of inescapable sin in a Christian’s life here, and at the beginning of the book. The later statements must be interpreted on the basis of what John presents here as a foundation.
But the Christian who sins has an Advocate with the Father. The "Christian" who does not sin may fend for himself, and good luck to him.
Christ is the propitiation for sins. Propitiation means the turning aside of wrath, which is why some translations omit the word—some moderns believe it is unseemly for God to be angry. But as Christians who believe the Word, we know it is unbecoming for us to provoke that wrath through our sins. Now Christ is the propitiation for the sins of the whole world. This means that the world will be saved. We must take both key words at face value here—both world and propitiation.