The heretics prided themselves on their imaginary wisdom and on supposedly possessing true knowledge, or faith, concerning God. From the Greek word gnosis, meaning knowledge, they were called Gnostics. At the same time, however, they led a sinful and sensual life, wholly attached to the goods of this sinful world.
In refutation of these heretics, the apostle writes that God is light, and in Him there is no darkness at all. For communion with God, a morally pure life is necessary. “If we say that we have communion with Him, and walk in darkness, we lie and do not act according to the truth.”
Communion with God requires constant care for one’s moral purity. For while living in the world, a man cannot remain sinless. Only by confessing his sins before God is he cleansed from defilement. “If we say that we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, then He, being faithful and righteous, will forgive us our sins and cleanse us from all unrighteousness” (ch. 1). For “we have an advocate with the Father, Jesus Christ the righteous. He is the propitiation for our sins, and not for ours only, but also for the sins of the whole world” (2:1-2).