It is clear that the false teaching which was affecting the churches to whom John was writing allowed its adherents to practice wrong behaviour. No matter how logical it seemed to them, it was evidence that they were not true Christians. There are several important deductions that we can make from John’s refutation.
First, there is the insufficiency of a mere verbal profession. We all know how common it is for persons in the public eye to profess an attitude and then for events to reveal that their conduct denied their claim. Countless politicians have endorsed particular ideas, such as supporting the importance of the family, and then been caught acting unfaithfully towards their spouses. The list of such incidents is almost endless. Yet the possibility of inconsistency is not limited to people outside the church. It happens within the church when a person who claims to be a Christian does not live a consecrated life.
Second, there is the implication of such inconsistency. John says that such a failure means the individual concerned is denying his profession in a twofold way: he denies it with his lips (his claim is a lie) and he denies it with his life. Now John is not describing a believer who falls into a temptation and then repents of it. His illustration is that of walking, which indicates a pattern of life. But it also indicates direction, of walking in a particular path. Those who walk in unholy practices are not walking with God.
The darkness in which such a person walks is both inward and outward. In a sense, the outward is easy to recognise – it is the world and all its sinful activities and ambitions. We can see such things and say that they are darkness. But there is also an inner darkness, a darkness of the heart. What would be the features of such a dark soul? The person in this state seldom thinks about God in his perfect character, seldom thinks about Jesus, seldom expresses love and thankfulness to him, seldom is concerned if his actions are grieving the Spirit, and exists happily without the fellowship of Christians.