Confession is a sign of regeneration, genuine conversion

But if we confess our sins, he is faithful and righteous, forgiving us our sins and cleansing us from all unrighteousness.1 John 1:9

The whole book of 1 John is written so that Christians can have assurance of their salvation (1 John 5:13). We don't have to confess our sins to be saved, God doesn't "forgive" us in a mystical sense, as if we could somehow be "forgiven" after having already been forgiven, and confession is not a method to be used in order to accomplish something. Simply put, confession in 1 John is one of the signs of genuine faith in Christ.

The problem with the "fellowship" interpretation

Those who believe 1 John is written about having "good fellowship" with God (being a "good Christian") would have several issues with 1 John. They would say, "See? If we confess our sins, then God will cleanse us of them." Thus, to them, confession is a way we can be brought back into "good fellowship" with God.

Ignoring God's forgiveness

The "good fellowship" view stresses the "cleansing" part while ignoring the "forgiving" part. A consistent "fellowship" interpretation would require the understanding that God's forgiveness of our sins depends upon our confession of them. This is absolutely heretical and contrary to the Gospel.

Misreading Scripture

John does not say that God will bring us back into good standing with Him, but that He will cleanse us from all unrighteousness. So, if we confess our sins, according to a consistent "good fellowship" view, God makes us completely and totally sinless.

1 John is not an instruction manual, but a litmus test

John is not telling us how to achieve anything. He is not writing an instruction manual. John's purpose in writing his letter is to give us a test that will tell us something very important about ourselves. His letter provides a mirror for us. What the test tells us, and what we see in the mirror is whether or not we are saved. John himself tells us this is what his purpose is:

I have written these things to you who believe in the name of the Son of God so that you may know that you have eternal life.1 John 5:13

In other words, John does not say, "If you do this, then this will happen." John says, "If this is true, then this other thing is true." An illustration:

A fish is turned into a human. But the ex-fish is unaware of the change. When you tell the ex-fish of what has happened to him, he doesn't believe you. To prove to the ex-fish that he is now human, you say, "Fish swim in water, men walk on the ground. If you say you're a fish, but you walk on the ground, you're decieving yourself." You continue, "A man does not breathe underwater, but breathe the air with his lungs. If you breathe air, you are a human."

In telling the fish that men walk on the ground, you are not telling the fish that he should walk on the ground in order to become a man. You are providing him with proof of what he truly is. Does he walk on the ground? Then he is a man. Does he swim in the water? Then he is a fish. John is giving us this kind of test to help us see something a bit less obvious to us than a fish-to-man transformation, but every bit as real. John is giving us a way to determine whether we have undergone the transformation from death to life, from sinner to saint, from lost to saved, from stubborn unbelief to genuine faith.

So John is not telling us to receive forgiveness by confessing our sins. He is telling us that genuine faith will manifest itself through a life of confession to God.

Ignoring proper tense

Poor translations may suggest that God will forgive us and will cleanse us if we confess our sins, but this is not true to the original Greek. A proper translation, as used on this page, says that God is forgiving us and is cleansing us (present tense), disproving the idea that John is telling us how to achieve something while strengthening the understanding that John is using outward signs to tell us something that is already true about genuine believers.