Light is shown in scripture to acts in two ways. Negatively, the light exposes man’s true condition (John 1:9; 3:20-21). This is what is meant in John 1:9, that He (the Son), "coming into the world, lightens" or illuminates "every man". His life of perfect righteousness and grace here is this world exposed the evil hearts of men. This is pictured in John 8, where Jesus declared "I am the light of the world", after He exposed the true moral state of the Jewish leaders who brought to Him the woman taken in adultery. But the light acts in another way too. Positively, the light gives us the knowledge of God’s character revealed in the Person of the Son (John 1:5; 2 Cor. 4:6). This is pictured in John 9, where Jesus again declared "I am the light of the world", and proceeded to open a man's physical and spiritual eyesight. It is a type of spiritual illumination through new birth. Unless a man is born again (John 3:5), he cannot see the kingdom of God. In that sense, the Divine life in Christ was "the light of men" (John 1:5).In 1 John being "in the light" is a positional thing, where "we walk in the light as he [God] is in the light", and in that position "we have fellowship with one another" (1 John 1:7).
Love and Light. These two words describe God’s essential character in different aspects. God is said to be light (1 John 1:5) and He is said to be love (1 John 4:16). To "be" something is far deeper that to "do" something. For example, God loves (John 3:16, etc.) but the expression "God is love" has a much deeper thought. Believers are commanded to "walk as children of light" and we are also said to be "light in the Lord" (Eph. 5:8). Light is the state and character of the divine nature, which we share by new birth. But believers are never said to "be" love. This is because love is a motive, a sovereign source that cannot emanate from man. God is sovereign in His love (agápe). As creatures, we are not sovereign. Only God Himself can be love, can be that source. We are privileged to be channels through which that love flows out. Hence, we are exhorted to “walk in love” (Eph. 5:5) and “love one another” (1 John 4:12). If it weren't for the Source, we could never love others with that same settled disposition; "we love because he has first loved us" (1 John 4:19). Light, on the other hand, is a fixed state of purity, and it is characteristic of our new nature.2
- Now God was light, perfect purity, which makes manifest at the same time all that is pure, and all that is not so. To have communion with light, one must oneself be light, be of its nature, and fit to be seen in the perfect light. It can only be linked with that which is of itself. If there is anything else that mingles with it, light is no longer light. It is absolute in its nature, so as to exclude all that is not itself. - Darby, J.N. Synopsis of the Books of the Bible.
- J. N. Darby. Love and Light. Notes and Comments, Volume 4, Page 233