Observation: As John dives deeply into the "light" metaphor of the Lord, and explicitly that God is pure light, and light means loving goodness, he makes statements about the proper way to live within that light. However, based on the language and structure, there are actually two different statements being made.
The first statement is about living a life "in the light" or living a life "stumbling around in the dark". A person cannot claim to be in the light while stumbling around in the dark. This seems to clearly be about faith and belief. As believers, we have faith in the Lord, and live a life in which we depend on his love, provision, blessing, and care. If we claim we have faith, yet do not live as if dependent upon the Lord, we are "lying through our teeth".
The second statement is about sin. It sounds the same, but the 'dynamics' are very different. In this case, if we claim we live without sin, we again are mistaken. However, there is no explicit or implicit expectation that we CAN live without sin. In fact, John is making the opposite statement ... that even as believers we DO sin, and we must not fool ourselves into thinking that somehow our faith makes our deeds sinless and perfect. Our faith gives us access to forgiveness, guidance, and correction, all of which is found in the person and teaching of Jesus.
Committing sin is not the same as "stumbling around in the dark". The dark is the place without the light of Yahweh, and our faith in him - a faith that changes how we consider living our lives - delivers us from darkness. We still sin, and our faith in Jesus gives us the mechanism to obtain forgiveness and continue our lives within the light.
Application: So often have I read this passage and believed John was making one statement ... that if we truly have faith, we will stop sinning. I have struggled with that, and not understood how it is possible. However, I now see these two concepts, and see how fundamentally important it is to understand them within the context of each other.
We have salvation through faith in Jesus, but that is also because it is that faith in Jesus as Messiah that allows us to have a relationship with the Lord. Without that, we cannot approach him ... we cannot be in the light. With the forgiveness found daily in Jesus, we can live in the light, receive his love and joy and bounty and mercy and justice and spirit. Then, if we live a life that actively turns aside from those things - rejects the Lord as our almighty creator and authority of our lives - we clearly are living in the evil darkness.
Prayer: Lord, I thank you for Jesus and for the path you have given us, by faith, to live in your light. Your love overwhelms me, and I worship you for your wonders and mercy and kindness and blessings that permeate my life. May I live in your light daily. In the name of Jesus, please forgive my sins this day and every day, so I may remain near you, in that glorious light. Amen.