John Gill emphasizes the significance of walking in the light as a reflection of being enlightened by the Spirit of God, which leads to a true understanding of sin and salvation through Christ. He explains that this walking in the light fosters a deep fellowship with God and with one another, highlighting the cleansing power of the blood of Jesus that removes all sin. Gill clarifies that this cleansing is not achieved through human efforts or rituals but solely through the sacrificial blood of Christ, which has eternal efficacy for believers.