Every verse of the Qurʾan has four senses: an outward (Zaahir) and an inward sense (Baatin), a limit (Hadd) and a point of transcendency (Matlaʿ).

The outward sense is the recitation and the inward sense is the understanding (Fahm) of the verse; the limit defines what is lawful and unlawful, and the point of transcendency is the heart’s place of elevation (Ishraaf) [from which it beholds] the intended meaning, as an understanding from Allah, Mighty and Majestic is He (Fiqhan Min Allah 'Azza Wa Jalla).

The outward knowledge [of the Qurʾan] is a knowledge [accessible to the] generality (ʿAam); whereas the understanding of its inner meanings and its intended meaning is [for] a select few (Khaas).

Thus Allah has said: What is wrong with this people that they fail to understand any words? [4:78] That is, they do not understand what they are being told.

- Imam Sahl al-Tustari
Tafsir al-Tustari