«وَلَا يُخَالِفُ ذَلِكَ لَفْظًا إِلَّا لِنُكْتَةٍ»
The apparent departure from this norm occurs for a rhetorical purpose.
The basic conditional relation concerns future occurrences, but Arabic may choose past forms, nominal clauses, or constructions whose ordinary tense value differs from the intended time.
Rather than dismissing this as irregularity, the rhetorical inquiry asks: why was this form chosen? Depending on context, the answer may involve certainty, strong desire, vividness, a firmly established cause, or another purpose. These do not all need to apply simultaneously.