The use of the term “light” to indicate “knowledge, integrity, intelligent, willing subjection to God, love to Him and to their fellow creatures, wisdom, purity, holy joy, rational happiness” as Jamieson, Fausset and Brown put it, is a well known device or idiom used as an illustration in Scripture. Light was to illuminate the darkness so nothing was hidden. David uses it in Psalm 36: “For with You is the fountain of life; In Your light we see light.” (verse 9). To understand the picture better, one needs to remember that the ancients believed it was light that travelled from the eye outwards, so that seeing (and understanding) was because the eye could light up the object, and furthermore, the eye was the window to the heart and soul of man. Plato wrote “As a breeze or an echo rebounds from the smooth rocks and returns whence it came, so does the stream of beauty, passing through the eyes which are the windows of the soul, come back to the beautiful on”. Therefore, the phrases such as the “lust of the eyes” and the “evil eye” etc. concern the heart, not the physical eye. Further, the light of the body was the eye – so if the eye was evil, it meant the whole body was evil, not the physical anatomical part of the body called the eye. Therefore, Matthew’s records Jesus’s comment that "The lamp of the body is the eye. If therefore your eye is good, your whole body will be full of light.” (Matthew 6:22). This makes perfect sense if one understands the eye as being the window through which the light from the heart can exit the body - so that through the eyes one sees the heart. Here, it is clear that Jesus is stating that if the eye is “shining” forth light, the heart cannot be darkness, but rather, the whole body is full of goodness, integrity, purity, holiness etc. In terms of Psalm 36 – our light is ever so dim; it is in the Light of the Saviour (Jesus Christ) that we see light”. We also see the eye responds to what the heart comprehends. For example: “The statutes of the LORD are right, rejoicing the heart; the commandment of the LORD is pure, enlightening the eyes” Psalms 19:8. Here the “enlightened” state is the comprehension of the distance man has fallen – his evilness, and thus understanding how sinful sin is: something the law told us.
The painting of the eyes (which is no modern invention) was to make the eye look more appealing, larger, more lustrous hence, speaking of the prostitution of the inhabitants of Jerusalem, Ezekiel writes: "Furthermore you sent for men to come from afar, to whom a messenger was sent; and there they came. And you washed yourself for them, painted your eyes, and adorned yourself with ornaments.” Ezekiel 23:40. In essence, the painting of the eyes attempted to distract one's attention from the dim light shining from the eyes, and hence the wicked heart that had no light in it.
Light was first created by God upon the earth which was without form and empty (Genesis 1:3). Its purpose was to divide that which could be seen from darkness. It was the first thing God considered God (1:4) and created on earth. It is by light that good and evil is shown up. Men lived in darkness (and loved it), but the Son of God was the light and would reveal to man the enmity between God the Father and him- or herself. The Light was divine revelation, both in the law of God, and Gospel of Christ; in order that humans could understand its lost state, and to comprehend the need for a Saviour, which Christ brought in person – the true gospel.
Here are the mentions of light in Gospel according to John
1:4,5 In Him was life, and the life was the light of men. And the light shines in the darkness, and the darkness did not comprehend it.
1:7-9 This man came for a witness, to bear witness of the Light, that all through him might believe. He was not that Light, but was sent to bear witness of that Light. That was the true Light which gives light to every man coming into the world.
3:19-21 And this is the condemnation, that the light has come into the world, and men loved darkness rather than light, because their deeds were evil. For everyone practicing evil hates the light and does not come to the light, lest his deeds should be exposed. But he who does the truth comes to the light, that his deeds may be clearly seen, that they have been done in God."
5:35 He was the burning and shining lamp, and you were willing for a time to rejoice in his light.
8:12 Then Jesus spoke to them again, saying, "I am the light of the world. He who follows Me shall not walk in darkness, but have the light of life."
9:5 As long as I am in the world, I am the light of the world."
11:9,10 Jesus answered, "Are there not twelve hours in the day? If anyone walks in the day, he does not stumble, because he sees the light of this world. But if one walks in the night, he stumbles, because the light is not in him."
12:35,36 Then Jesus said to them, "A little while longer the light is with you. Walk while you have the light, lest darkness overtake you; he who walks in darkness does not know where he is going. While you have the light, believe in the light, that you may become sons of light." These things Jesus spoke, and departed, and was hidden from them.
12:46 I have come as a light into the world, that whoever believes in Me should not abide in darkness.