وَإِنَّ عَلَيْكُمْ لَحَـٰفِظِينَ
Sentence structure
In the emphatic clause, عَلَيْكُمْ is the fronted predicate of إِنَّ, and لَحَـٰفِظِينَ is its delayed accusative noun; the lām adds emphasis.
Ayah summary
Angels have been appointed over you to watch your deeds.
وَإِنَّ — And indeed
Grammar: وَ resumes the discourse and إِنَّ is an accusative/emphatic particle.
عَلَيْكُمْ — over you
Grammar: A prepositional phrase functioning as the fronted predicate of إِنَّ; attached كُمْ is genitive.
لَحَـٰفِظِينَ — (are) surely guardians
Grammar: لَ is the displaced emphatic lām. حَـٰفِظِينَ is an active participle and the delayed noun of إِنَّ, accusative with yā because it is a sound masculine plural; its final nūn is the nominal plural ending, not a verb-mood marker.