The Christian is not a man or woman who ought to be walking in the light but who so often is walking in darkness. The Christian is one who, by definition here, is always walking in the light even though he falls into sin. By falling into sin you do not return to walking in darkness. The Christian is not a Christian unless he is walking in the light. (pg. 129) Christians do not spend their lives walking in and out of the kingdom of God; we are all by nature in the kingdom of darkness and by becoming Christians we are translated, put into, the kingdom of God. (pg. 129)
I am not walking in darkness because I have sinned; I am still in the the kingdom of God even though I have sinned - the shed blood of Jesus put me there. And it is this shed blood that still delivers me from the guilt of my sins in the kingdom of God. (pg. 129 - 130)
All quotes taken from Fellowship with God by Martin Lloyd Jones ©1993 by Bethan Lloyd Jones and published by Crossway.