What is the significance of the metaphor of light in the Gospel of John? Please add examples. Thank you very much!

Light had been a very important metaphor in culture and religion long before the Gospel of John was written. Light was God; light was wisdom; light was hope; light was supernatural illumination. The metaphorical use of light was one of many significant bequests left to the early Christians by Judaism, and the Old Testament is suitably replete with examples:

But the path of the just is as the shining light, that shineth more and more unto the perfect day (Proverbs 4:18; KJV).

Unto the upright there ariseth light in the darkness: he is gracious, and full of compassion, and righteous (Psalm 112:4; KJV).

Light is sown for the righteous, and gladness for the upright in heart (Psalm 97:11; KJV).

There are primarily two ways that light is used in the Gospel of John. First, it is used to present us with a stark choice of how we ought to live our lives; should we live in darkness or in light?

For every one that doeth evil hateth the light, neither cometh to the light, lest his deeds should be reproved.

But he that doeth truth cometh to the light, that his deeds may be made manifest, that they are wrought in God (John 3:20-21; KJV).

We need to make a decision. Moreover, the terms set out in the Gospel of John make it pretty clear what the consequences of that decision will be.

However, the process of seeing the light is a gradual one, and the metaphor of light amply reflects that journey. The light is always there; we just do not always live our lives in it. Light, therefore, is presence. God himself is always present, but we often do not acknowledge Him. This point is illustrated by the parable of the blind man in John 9:5. A poor man has been blind since birth, and Jesus heals him. Before he does so, Jesus declares,

As long as I am in the world, I am the light of the world (John 9:5; KJV).

However, the blind man's healing is only the first stage of his faith journey. Not only must he see, he must also believe:

Jesus heard that they had cast him out; and when he had found him, he said unto him, Dost thou believe on the Son of God?

He answered and said, Who is he, Lord, that I might believe on him?

And Jesus said unto him, Thou hast both seen him, and it is he that talketh with thee.

And he said, Lord, I believe. And he worshipped him.

And Jesus said, For judgment I am come into this world, that they which see not might see; and that they which see might be made blind (John 9:35-39; KJV).

A further example is provided when Mary Magdalene discovers the empty tomb. She goes there while it is "yet dark" (John 20:1; KJV). Christ then eventually appears, but she does not recognize him until he speaks her name:

Jesus saith unto her, Mary. She turned herself, and saith unto him, Rabboni; which is to say, Master (John 20:16; KJV).

In the Gospel of John, light also means spiritual enlightenment. The light of Christ is the "true" light. Light in this sense is hyperreal, representing a higher spiritual reality and one that stands in contrast to the merely earthly and contingent. We can observe here the profound influence of Greek philosophy upon early Christianity, especially in the Gospel of John, generally regarded as the most overtly philosophical of the four Gospels. As with Plato, what is ultimately real in Christianity is the spiritual and the transcendent, not the physical world of everyday life. The light of Christ, according to John, is the ultimate reality:

I am the true vine, and my Father is the husbandman (John 15:1; KJV).

Light is also a symbol of judgement, used to expose the darkness of error, falsehood, and sin. Jesus shows this in his conversation with the Pharisee Nicodemus:

And this is the condemnation, that light is come into the world, and men loved darkness rather than light, because their deeds were evil.

For every one that doeth evil hateth the light, neither cometh to the light, lest his deeds should be reproved.

But he that doeth truth cometh to the light, that his deeds may be made manifest, that they are wrought in God (John 3:19-21; KJV).

The light of Christ does not just expose evil, it simultaneously illuminates the truth. The judgement it represents is like all of the metaphorical uses of light we have discussed: it is there to guide us toward the ultimate truth, through which we will be saved.