Tafsir of Qaf 50:33

(33) He who fears the Most Merciful in the unseen and comes with a repentant heart.

This is a substitution for "the God-fearing" (al-muttaqin), or a second substitution for "the God-fearing," based on the permissibility of having multiple substitutes for the same substituted-from noun (mubdal minhu). The statement of Abu Hayyan—that repeating the substitute for a single substituted-from noun is impermissible except in the case of a substitute of rectification (badal al-bada’), and that its logic is that the [initial] substituted-from noun is intended to be discarded and thus cannot be substituted for again—is not accepted. Ibn al-Hajib permitted it in his Amali, and al-Damamini reported it at the beginning of his commentary on al-Khazrajiyyah and spoke at length upon it. The notion that the substituted-from noun is intended to be discarded is not taken at its literal meaning.

Alternatively, it is a substitute for a described entity (mawsuf), meaning "for every penitent person," based on the permissibility of omitting the substituted-from noun. Ibn Hisham permitted this in al-Mughni, especially since its description has taken its place, such that it is as if it were not omitted. It is not a substitute for "penitent" (awwab) itself, because "penitent" is an adjective for an omitted noun, as you have heard; if it were a substitute for it, the substitute would possess a wisdom and thus be an adjective like it.

"He" (man) is a relative pronoun, and relative pronouns do not function as adjectives except for "that which" (alladhi) according to the more correct view. Some have permitted describing with "he" (man) as well, but this is a weak view. Alternatively, it is an initiating subject (mubtada’) whose predicate is [yet to come].