Jesus said "While I am in the world, I am the light of the world".

The blind man's eyes did not know the light of the world, but Jesus knew that it was he who was the true light of the world - Jesus gave the light of the world to the man's eyes by mixing his saliva/body with the mud/earth/world and applying that mixture (of Jesus in the world) to the mans eyes, and they saw light.

So, God's work was to testify to Jesus' authenticity - that he is the light of the world - and this was done perfectly here by the healing of the blind man.

The healed blind man, by proclaiming that Jesus healed him with mud made from his saliva was actually proclaiming that Jesus was the light of the world although he did not know about Jesus' divine significance.