Tafsir of At-Takweer 81:28

{For whoever among you wills} is a badal (substitutive) for {the worlds}, specifically a badal ba'd min kull (part-whole substitution), and the badal is the prepositional phrase. The governing word (‘amil) is repeated with it, according to the well-known view. It is also said that it is the preposition and the governed noun together. It is permissible that it be a badal kull min kull (total substitution), by treating those who do not will as beasts through metaphorical attribution, though this is forced interpretation.

His saying, the Exalted, {to take a straight course} is the object of the verb "wills." That is, for whoever among you wills uprightness by seeking the truth and adhering to what is correct. It is made a badal for {the worlds} because they are the ones who benefit from the reminder.