"If we say that we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, he who is faithful and just will forgive us our sins and cleanse us from all unrighteousness" (1 John 1:8-9).
The two 'letters of John' are really more like essays; they're not addressed to a specific church, but generally to followers of Jesus. Written in the final years of the first Christian century, the main purpose seems to be to correct what the author perceives to be misunderstandings and false teachings. These two verses follow the extraordinary statement that "God is light, and in him is no darkness at all" (verse 5). It is by walking in the Light of faith that all shadows within us—fears, habits, false beliefs—will be dissolved as we follow the example of Jesus.
In Unity, we understand 'sin' to be 'error thought.' It is a word that represents the choices we make that do not recognize and affirm our oneness with divine Truth. We have all made negative choices, accumulating in the process the shadows in consciousness that make life more challenging than it needs to be. To deny that simple Truth essentially blocks us from the Light—we can't dissolve shadows if we refuse to acknowledge that there are any shadows! It is by recognizing the shadows within, bringing them into the Light, that we dissolve their ability to disturb our consciousness.