‘When he had thus spoken he spat on the ground, made clay with the spittle and anointed the his eyes with clay.'
The fact that Jesus was able to put the clay on the man's eyes demonstrates that there was already some faith in the man's heart. The man was willing for Him to do it. He would have been told who this was who wanted to do this thing, and he gave his consent. Then he waited patiently while the process was carried out.
It is true that spittle was looked on as an ancient medicine, and because of this some have suggested that this was an aid to faith for the blind man, but it is evident from previous healings that Jesus did not need to resort to such methods, and it is therefore far more likely that we are to see it as symbolic of His word of power coming from His mouth opening the eyes of the spiritually blind. It also demonstrated that he required active faith from the man. The man could do nothing towards his healing, but he could refuse or show willingness to respond to Jesus' word. We too can do nothing towards the opening of our spiritual eyes, but whether we respond or not will be determined by whether there is faith in our hearts.