This is fairly close towards the end of Jesus life at this stage of the Gospel of John. There had been a gradual growing of understanding of the disciples of who Jesus was. Nobody at this stage was really questioning the fact that Jesus was quite remarkable, but probably nobody really understood that He was actually God in the flesh.
Without God to give life, there is absence of life. Without God to give light, there is darkness. Light and darkness is also a picture of good and evil. Jesus said ‘I am the Light of the world’.