What is the principal rhetorical effect of the fāʾ in fa-l-mūriyāt and fa-l-mughīrāt?

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

• Cancelling the wording of each previous oath
• Conveying succession and rapid development in the scene
• Necessarily converting the agent into passive voice
• Making each noun a cognate accusative