Tafsir of Al-Baqarah 2:175

(Those are they who purchased) on account of their concealing the truth for base cravings and worldly purposes, (error with guidance) in this world, (and the punishment with forgiveness) in the Hereafter.

The sentence is either:

1. Inceptive (Musta’nafa): Since the threat to the concealer was magnified, it was expected that one might ask about the reason for the intensity of their threat. It was thus said: "Indeed, by their concealing, they have lost both the world and the Hereafter."
2. A predicate after a predicate: Because the first sentence serves to illustrate the severity of their threat, and this one serves to illustrate the heinousness of their concealment.

(So what makes them so patient for the Fire?) That is: "How intense is their patience?" It is an expression of amazement for the believers regarding their commission of the acts that necessitate it [the Fire] without any regard. Otherwise, what patience do they truly have?

Regarding "what" (mā) in this structure:

• It is said to be an indefinite complete noun (nakira tamma), and this is the position of the majority.
• It is said to be interrogative (istifhamiyya) imbued with the meaning of amazement, which is the view of al-Farra’.
• It is said to be relative (mawsula), which is the view of al-Akhfash. It is also narrated from him that it is an indefinite described noun (nakira mawsufa).

Based on these views, it is in the nominative case as an inceptive (mubtada’), and the [following] sentence is its predicate, or its predicate is omitted if it is a modifier (sifa) or a relative clause (sila). The complete discussion on this is in the books of grammar.