The heck?
The character and use of most ordinary oils includes medicinal and healing uses. This was obvious to a pre-modern person – even if we are ignorant about it, because we have different medicines.
Blessing an oil is a way of claiming it for God, helping the creature oil (as the older forms of blessing address the oil) serve God more fully.
Miraculous healing by God through a blessed oil is not superstitious unless people treat it as a vending machine, instead of a sacramental and a gift from God. But being healed by a blessed oil would be within the range of stuff that often happens. It is not normal oil; it is a sacramental – oil dedicated to God and working for Him.
Look. God made matter. It was His invention and creation. Jesus Christ is God, and became man. He became matter. It was His special way to.approach us.
So of course He was going to include matter in His miracles. It was a sign for us, and it indicated His role as the New Adam, in charge of earthly creatures.
Also, it was fun and thematically appropriate. Mud over the eyelids or painted on the face like a football player, was a common way to soothe eyestrain, so using it for blindness was like using a Band-Aid to instantly heal a sucking chest wound – impressive. It goes to the tradition that the Messiah would provide heavenly medicine and balm, and the mud has other implications too that I cannot remember.
Basically, Jesus knew what He was doing, and His signs make clear statements if you are a Biblically knowledgeable Jew of that time. Which is why He made.people so angry. They understood what His signs and miracles were saying, and they did not like it.
