Grammatical validity and rhetorical purpose are distinct questions. Not every word order is grammatical. Where two acceptable structures exist, the speaker chooses the one that better suits the occasion.
Example 1: ظَهَرَ الْهِلَالُ — The new moon appeared.
Example 2: الْهِلَالُ ظَهَرَ — The new moon: it has appeared.
Both report the moon’s appearance. The first is a verbal sentence. In the second, al-hilal is the initial subject, while zahara with its implicit subject forms its predicate. This arrangement allows topical prominence and a second predicative connection.