The phrase fī athnāʾ al-kalām refers to an insertion before the surrounding construction has finished. If the parenthetical clause is removed, the remaining constituents recover their original syntactic relation.
A parenthesis may stand between subject and predicate, a governing verb and a related element, or another pair of connected parts. Its rhetorical suitability depends on preserving the main predication while adding an independent supplication, reminder, explanation, or comparable benefit.