John gets down to the basic of the basics. I remember an old song that talked about calling it like you see it, and this is the case here. Does the check list get any more straight-forward? If you do right, it is self-evident that you are righteous (because God has made you so). And if you live a life of sin... well, you're on the losing team. John makes it clear here, however, when he says, “whoever makes a habit of sinning,” as opposed to just “whoever sins.” We all sin, for we are fallen creatures in a fallen world. Even as a new creation, we are still affected by the world around us and the flesh we still are wrapped in. This is grace at its finest, that He not only saves us in the first place but He then continues to pick us up and carry us when we fall short. But it is when sin still prevails in our lives that we need to be concerned. It is when our desires hold our attention more than God that we need to wonder about our relationship with Him who is righteous.
We have seen throughout this letter that there is in God no room for sin, and here John clarifies exactly who sin belongs to. He says it's the devil's and he's the master of it. If the focus of our life is sin, then we are certainly not living in association with God, but with the devil! But it also says in this verse that Jesus came to destroy the work's of the devil – to break the bonds of sin. So if, on the other hand, we give our life to Christ and let him do what he's good at, we can have victory over sin. We can actually live in habits of righteousness and be confident in our relationship with the Father, who is righteous.