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).
The Light. A vast and important subject in scripture is that of light. The word has two primary meanings. First, 'light' can refer to a character or state of absolute moral purity. We read that "God is light, and in Him is no darkness at all" (1 John 1:5). Light is the character of God's own nature. He is perfectly pure. Furthermore, all of God's associations are pure, and therefore He is unapproachable by man in the fallen condition; "dwelling in unapproachable light; whom no man has seen, nor is able to see" (1 Tim. 6:16). When, by God's action of quickening, a sinner is given divine life, they receive a nature that is holy, although they still have the flesh. "For ye were once darkness, but now light in the Lord" (Eph 5:8). We have a nature that is perfectly pure, although "walking as children of light" is a matter of communion and obedience. In 1 John it is a positional thing, where "we walk in the light as he [God] is in the light", and therefore "we have fellowship with one another" (1 John 1:7). The second way 'light' is used has to do with what light does. Light reveals things. The principle is given in Eph. 5:13; "But all things having their true character exposed by the light are made manifest; for that which makes everything manifest is light." When the Son of God came into this world, He became "the Light of the World". The light had an effect on men.
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.