"On the one side, you don't keep on sinning if you're born again. On the other side, you don't ever stop sinning in this world. In other words, John is trying to strike a balance between the absolute necessity of the new birth, which necessarily gives a significant measure of victory over sin. That's the one side. On the other hand, there's the reality that we do in fact as Christians commit sins and can find forgiveness as we confess them." - John Piper