What does the khayran/sharran contrast accomplish in 99:7–8?

Supplementary Practice 25 — Comparative Rhetoric of Sūrat az-Zalzalah and Sūrat al-ʿĀdiyāt

• It establishes that the two words are synonyms
• It states accountability for both good and evil through parallel structures
• It makes the second condition abrogate the first
• It renders the scale of deeds wholly irrelevant