Tafsir of Ghafir 40:70

(Those who denied the Book): That is, the entire Quran or the category of heavenly scriptures, for denying it constitutes a denial of them all. It is in the genitive case as a substitute for the first noun described [the disbelievers mentioned previously], or as an elucidation, or as an adjective for it. Alternatively, it is in the accusative case due to disparagement [implied "I censure"], or in the nominative case as the predicate of an omitted subject, or as a subject whose predicate is (then they will come to know).

The second relative pronoun [i.e., "those who"] is connected to "denial" rather than "disputation" because disputation usually occurs in some matters, not all, whereas denial encompasses the entirety. The past tense form is used to indicate certainty, just as the present tense form in the first relative clause [i.e., "those who dispute"] is used to indicate the renewal and repetition of disputation.

(And [denied] what We sent Our messengers with): This refers to all the scriptures according to the first interpretation of "the Book," or to absolute revelation and religious laws according to the second interpretation.

(Then they will come to know): The essence of what they committed by way of disputation and denial when they witness His punishments.