If we say that we have fellowship with him and walk in the darkness, we lie, and don't tell the truth.
we lie, and do not the truth: How much more emphatic can the apostle be? If we propose to say that we are walking in fellowship with God and living in sin at the same time, we are lying and are not practicing the truth. The Gnostics were telling this lie and practicing this untruth. They thought the body was just a simple envelope housing the spirit and could not contribute to the contamination of the spirit on the inside. 