وقد ينزل المخاطب العالم بهما منزلة الجاهل
An addressee who knows both the judgment and the speaker’s awareness may be addressed as though ignorant because their conduct does not accord with what they know.
Someone understands the obligation of prayer but persistently neglects it. Saying «الصَّلَاةُ وَاجِبَةٌ» in admonition does not merely teach an unknown rule. It directs attention to the failure to act on known truth.
This is tanzīl al-ʿālim manzilat al-jāhil: treating the informed as uninformed for a rhetorical purpose, not literally denying that all knowledge is present.