“God is light, and in him is no darkness at all… if we walk in the light… the blood of Jesus his Son cleanses us from all sin”. John’s message is one of an eyewitness, who observed and loved the only perfect manifestation of God’s light by a human.
John pleads with his readers to keep God’s word, the word of life. Those who wish to do so should “walk in the same way in which [Jesus] walked”, love the Father, and abide in the Son and the Father. This attitude and love must pervade every aspect of our life, as surely as light drives away darkness.
John’s motivation for sharing this advice was that his “joy may be complete”. How much more joy will our Father feel, if we, His children, demonstrate perfect love by keeping His commandments.