Jesus spits on the ground, makes clay from the saliva, places it on the blind man's eyes, and tells him to wash in Siloam. To modern readers the procedure can seem especially strange.
Saliva, however, was sometimes credited with healing properties in the ancient Mediterranean world.
Ancient Jewish and Greco-Roman sources preserve examples of saliva being used or discussed in therapeutic and popular healing contexts. The evidence does not establish one standardized ritual that Jesus is simply following. Mixing saliva with earth to form clay also makes the action visible and tangible.
John later emphasizes that making the clay occurred on the Sabbath, turning the action itself into part of the controversy.
The cultural background makes the material action less alien without explaining the healing away. The man was blind from birth, and the narrative attributes his sight to Jesus.
As elsewhere in the Gospels, Jesus can employ familiar physical means while the effectiveness of the sign points beyond those means to his authority.