John began his first epistle with the declaration that the eternal has been manifest in the flesh in Christ and because of the incarnation we have fellowship with God and with one another. But sin breaks fellowship, so through the rest of 1 John chapter 1 he was addressing some errors of our understanding of sin - it's not a big deal, we don't really sin anyway, and God doesn't care about it too much. All of these are deceptions and he speaks to each one in order that we might test ourselves so that we would have fellowship with God and with one another. Well, John continues to address the issue of the revelation and fellowship of light and love through some tests - a moral test, a social test and a doctrinal test. John is intent all throughout to speak to temptations of his day to give up on some of these basics of the faith