Matthew 5.14-16:
You are the light of the world. A city set on a hill cannot be hidden. (15) Nor do people light a lamp and put it under a basket, but on a stand, and it gives light to all in the house. (16) In the same way, let your light shine before others, so that they may see your good works and give glory to your Father who is in heaven. (ESV)
So we know that Jesus himself is the light of the world. And Jesus teaches in the verses above that his disciples are also the light of the world. There is the appearance of a little logical tension between these two truths, and so we should seek to understand how they both are true. There is scholarly treatment of these verses that takes note that John 8.12 is stated literally because Jesus himself, as the creator of the universe, is the ultimate expression and reality of light. So when we read in Isaiah 9.2 and Matthew 4.16 that a “light” has dawned, there is more meant by this word than just a figurative way to refer to Jesus as the Messiah.
But the teaching of Matthew 5.14 is spoken within a figurative context because it is used in conjunction with the statement in Matthew 5.13 that Jesus’ disciples are also the salt of the earth. The figurative nature of this usage appears to apply to the way Jesus’ disciples should live their lives, striving to walk in the light and living in accordance with the teaching of Jesus. This would be in keeping with verse 16 where Jesus makes reference to “your good works”. The “light” has its application in our lives, because there is no darkness in the presence of Jesus and his teaching of righteousness.