Why are “ghafara Allāhu laka wa-raḥimaka” not simply two reports about the past in a setting of supplication?

Supplementary Practice 7: Editing Expressions, Weighing Context and Rhetorical Critique

• Past morphology serves the semantic function of prayer or request
• Both explicitly use imperative morphology
• Supplication never uses past morphology
• Wāw invariably turns expressions into reports