This is the message which we have heard from him and announce to you, that God is light, and in him is no darkness at all.

 Here John is writing to counteract one heretical way of thought. There were those who claimed to be specially intellectually and spiritually advanced, but whose lives showed no sign of it. They claimed to have advanced so far along the road of knowledge and of spirituality that for them sin had ceased to matter and the laws had ceased to exist. Napoleon once said that laws were made for ordinary people, but were never meant for the like of him. So these heretics claimed to be so far on that, even if they did sin, it was of no importance whatsoever. In later days Clement of Alexandria tells us that there were heretics who said that it made no difference how a man lived. Irenaeus tells us that they declared that a truly spiritual man was quite incapable of ever incurring any pollution, no matter what kind of deeds he did. 