God's Word is truth
"The light" is the truth. God's Word is truth (John 17:17). We have to walk in the light "as He is in the light." He lives in us, and we in Him. We are in union with Him.John is telling us how we become clean: We become clean as we apply God's Word. It gets in us and begins to clarify and purify our thinking. But it does not become a real cleansing until it begins to be used. Then, it begins to clean up our bad habits and thinking processes. The thinking processes change according to our action, our behavior. If we keep doing the same things all the time, nothing changes. We are resisting. "Walking" denotes living. If we live as He lived, then we become cleansed. This is what holiness is. If we do that, then we will produce fruit—it is impossible not to!