Ghurūr: being fooled by your own accomplishments
Al-Ghazali saw this happen most often to scholars. Someone masters every argument about God, and the mastery becomes the thing they love, while the heart it was meant to open stays shut. From the inside it feels like progress, because being good at the subject is easily mistaken for being close to God.
Being unable to grasp Him is itself a grasp of Him: where thinking runs out
The Sufis repeat this line from Abu Bakr. Anyone who thinks hard enough about God hits a wall, and the usual move is to paper over it with a better definition. Owning the wall does more: the person stops shrinking God to the size of their own head, and something in them goes quiet and open.
Dhawq: tasting, knowing a thing by going through it
Al-Ghazali landed on this word after years of lecturing about God. He compared it to the difference between reading about honey and putting some in your mouth. No description carries a person across, which is why a plain report from someone who has tasted can sound like nothing to someone who has only studied.
Nūr: light, the knowing that arrives rather than the knowing you build
Al-Ghazali said the knowing he wanted came as a light God threw into his chest. He had done all the work and the work had not produced it, so he understood the thing as a gift and not a wage. That is why it can land on someone plain and pass over someone brilliant; no amount of ability makes it owed.
Sell your cleverness and buy bewilderment: what looks like a bad trade
Rumi puts it as a purchase. Cleverness keeps an answer ready for everything, which protects a person from ever being caught out, and therefore from ever being changed. Bewilderment costs that protection, and giving up the look of knowing means accepting that some people will think less of you. In exchange, something new can finally get in.