لِتَبَادُرِ الْفَهْمِ عِنْدَ سَمَاعِهَا
Because its meaning immediately occurs to the hearer.
Tabādur is the readiness with which a particular sense is understood when a form is heard without a special contextual cue. The immediate sense of ifʿal normally is “perform the action.”
Yet this does not prohibit a transferred reading. Evidence of a threat, impossible challenge or humiliating address can make a different purpose clear. Grammar identifies the morphology; rhetorical analysis identifies the intended speech act in context.