I know of nothing in the Bible that explains the following, but perhaps you can provide some insight.
Why did our Lord use spittle and clay to heal the blind man instead of merely speaking the word? What lesson are we to learn from that?
You’re referring to John 9:1-12. I think the Lord was making a point about working on the Sabbath. This is borne out in John 9:13-16 by the fact that the authorities were upset that he had “made mud and opened the man’s eyes” on a Sabbath.
The Pharisees held that if you spit on the Sabbath and your saliva landed on a rock, you were OK. But if it landed in the dust you were guilty of making mud. Jesus went further by purposely mixing the saliva and the dust together so that there would be no doubt that He was working on the Sabbath, according to their interpretation of the Law.
This led to His accusation that they were spiritually blind, and couldn’t see that they could only enter the Kingdom through Him, no matter how obsessively they kept the Law.
John used this format seven times in writing his gospel, beginning with a miracle, followed by a discourse, and concluding with an “I am” statement.