Sirr: The innermost secret in a person
The sirr is the deepest layer inside someone, closed off to everyone outside it. A close friend can watch you for years and still guess wrong about what you carried around all morning. That lock opens from the inside, which is why nobody arrives at God by examining God from the outside.
Whoever knows himself knows his Lord: knowing begins from the inside
Sufis repeat this saying constantly. Watching your own wanting and fear long enough teaches you how a hidden thing gets known at all, which is from within it. Someone who has never looked honestly at their own inner life has no feel for how God could be known either.
None knows God except God: the knowing comes from God's side
Ibn Arabi returns to this line again and again. Any picture of God a person assembles is built from pieces they already had, so it ends up a portrait of their own mind. The strain lifts when they stop defending that picture and let the knowing come from God rather than from their own effort.
Ilm ladunnī: Knowledge given straight from God
The Quran tells of a servant taught knowledge from God's own presence, and al-Ghazali wrote a whole treatise on it. Such knowing turns up as a settled certainty that a person did not build and cannot trace to any book or teacher. Books and teachers prepare the room, and then the knowing arrives, like an answer that comes after you stop chasing it.
Dhawq: Knowing by tasting
Dhawq, the word for tasting, covers what you can only learn by going through it. Al-Ghazali put it plainly: knowing the definition of being drunk leaves a person stone-cold sober, and descriptions of honey never hand over the flavor. The things of God work the same way, learned by having them, so no account from outside passes them along.