What is the significance of Jesus' spitting on the ground in the book of John? Why does Jesus spit on the ground and make clay to anoint the blind man's eyes?  What does this represent?  Is the need to wash the anointing off significant?

John 9:6-7 NIV


  After saying this, he spit on the ground, made some mud with the
  saliva, and put it on the man’s eyes. “Go,” he told him, “wash in the
  Pool of Siloam” (this word means “Sent”). So the man went and washed,
  and came home seeing.
I will represent the Roman Catholic position on the verse.

Historically, St. Thomas Aquinas noted that this verse provided an example of Jesus' healing of sin. He cites St. Augustine for the interpretation that the blind man represents the human race. Sin is the spiritual blindness. When Jesus heals the blind man and allows him to see the light, he literally sees, which can be taken as a sign that he sees the error of his ways and wants to correct them by following the ways of God.1

Additionally, St. Augustine, the early church father, wrote that the clay represented the anointing, and the blind man represented the catechumen, because he was anointed but not yet washed. So, I wouldn't really say that it's washing off the anointment, because it may be the effect of the anointment that healed the blindness or sinfulness. The washing is to emphasize that the blind man is no longer a catechumen, or that he is a baptized believer.2 Meanwhile, the physical clay-and-spit is washed off, probably because that would be an eye irritant.

Source:


http://dhspriory.org/thomas/John9.htm 
http://www.newadvent.org/fathers/1701044.htm