The claim to be a Christian may be variously stated, in terms of knowing God (4), or living in Christ (6) or being in the light (9), but invariably, if it is an authentic claim, it will show itself in a new life of obeying God (4), imitating Christ (6) and loving our brothers and sisters (9–10). Without such a moral authentication, the claim is seen to be bogus.
JRW Stott. The Letters of John.