Omission of the subject (حذف المسند إليه) occurs when the person or thing about which a predication is made is not explicitly named, while sufficient evidence still identifies it. Ellipsis is not merely a device for shortening: leaving an understood item unspoken can itself be rhetorically effective.
أما حذفه فلأمور
Its omission can serve several purposes.
If someone asks «كَيْفَ زَيْدٌ؟» (‘How is Zayd?’), the answer «مَرِيضٌ» (‘[He is] ill’) may stand without repeating Zayd's name. The question identifies the subject. But addressing a person who has no such context with the bare predicate may fail to communicate the intended information. Successful ellipsis depends on an indication.