Nafs: The lower self
Nafs names the part of a person that weighs everything by what it gets back. Someone living from there can be sharp and well read and still hear nothing in talk about God, because it pays no return their scale can read. The blankness is honest; nothing inside them picks the signal up.
Rust has settled over their hearts: how a person lives dulls the part that sees
The Quran says the heart rusts over from what a person keeps doing. Small choices, repeated, leave a film on the one part that could have caught this, and the dulling is too slow to feel. Afterward a person cannot tell a message that is over their head from a message that is nonsense, so they call it nonsense.
The reasoners walk on wooden legs: argument by itself cannot carry a person here
Rumi wrote that the legs of the arguers are wooden legs, and wooden legs are unsteady. His point was about range, since reasoning works over a certain distance and wobbles past it. Someone whose only instrument is argument keeps testing these things by argument, watches them fail, and decides they are foolish.
Dhawq: Tasting
Dhawq means knowing something by having had it, the way a person knows honey by tasting it. Al-Ghazali kept pointing out that someone can hold a perfect definition of drunkenness while stone cold sober. God's things are known along that road only, so an outsider can repeat every word about them accurately and still hold nothing.
Kashf: Unveiling
Kashf means the covering lifting so that the heart sees for itself. It comes as a gift, which is why no amount of cleverness forces it and no argument installs it in another person. The difference between two people here is not more information; one has been given an eye for it, and that eye does the receiving.