In William W. Combs‘s “The Meaning of Fellowship in 1 John” (a twelve-page article that he presented last week at the 2007 Mid-America Conference on Preaching at Detroit Baptist Theological Seminary), he reaches two conclusions:

1. “We do not confess our sins to maintain fellowship with God. Fellowship with God is the privilege of all genuine believers because it is nothing less than the sharing of eternal life with God and other believers. As believers we confess our sins because sin is still an affront to God. And even though it does not diminish our standing in justification before God—we will always be his children, members of the family of God—sin does affect our relationship in the family. God is working sanctification in us—progressive sanctification—we are progressing in holiness, and that means being set apart from sin, mortifying sin on a daily basis, and that involves confession—agreeing with God that sin is evil and wicked—and a determination to turn and forsake it. A genuine Christian will have a sin-confessing attitude. Certainly it is true we can backslide and become carnal for a time. But ultimately a true Christian will repent and confess his sins to God. Those who do not have no reason to be assured of their salvation.”
2. “So you ask, ‘What do you call it when a Christian sins?’ I do not call it anything except sin. Others speak of it as being out of fellowship, and I generally do not go around telling them they are wrong, trying to correct them. But I myself usually refrain from saying sinning Christians are ‘out of fellowship,’ since that is not how John uses the term. This in-and-out-of fellowship terminology is also deficient because it views all believers as being in either one of two tiers or levels. Either he is in or he is out of fellowship. There are not just two levels in the Christian life; there are thousands and thousands of levels. That is why we speak of progressive sanctification. It is simplistic to try to describe a believer as being either/or, though I recognize sometimes it seems necessary, and I probably do it myself. But in truth the Christian life of sanctification is a constant, daily, and progressive dealing with sin in our lives. It cannot be reduced to only two levels or tiers. There is no such thing as being in fellowship with God where one is ‘walking in the light’ and not committing any sins. Anyone who thinks so has a weak view of sin and an under appreciation of his own depravity. This does not mean that the Christian life is one big negative ball of sin. There is victory over sin in the Christian’s life—victory over the dominion or the reign of sin in our lives. Sin no longer dominates our lives as it does the unbeliever. But we must still do battle with sin everyday, and that involves confession to God where we fail. The genuine believer will have a sin-confessing attitude. And if we do, it gives us assurance that we truly have fellowship with God, that we are genuine
   believers.”