إِنَّهُۥ لَقَوْلٌۭ فَصْلٌۭ
Sentence structure
The complete clause is the response to the preceding oath. Attached هُۥ is the noun of إِنَّ. In لَقَوْلٌۭ, لَ is emphatic and قَوْلٌۭ the nominative predicate; فَصْلٌۭ is its matching adjective.
Ayah summary
The Qur’an is a decisive word that distinguishes truth from falsehood.
إِنَّهُۥ — Indeed, it
Grammar: إِنَّ is an accusative/emphatic particle and attached هُۥ its third-person masculine-singular noun.
لَقَوْلٌۭ — (is) surely a Word
Grammar: لَ is the emphatic lām; قَوْلٌۭ is an indefinite nominative verbal noun functioning as the predicate of إِنَّ.
فَصْلٌۭ — decisive
Grammar: An indefinite masculine-singular nominative adjective of قَوْلٌۭ.