فَلَآ أُقْسِمُ بِٱلشَّفَقِ
Sentence structure
فَ resumes the discourse and لَآ is a non-governing negative particle whose precise rhetorical force has more than one accepted explanation. أُقْسِمُ is a first-person imperfect, and بِٱلشَّفَقِ is linked to it.
Ayah summary
An oath is sworn by the twilight glow.
فَلَآ — But nay
Grammar: فَ is resumptive and لَآ a non-governing negative particle; its precise rhetorical force is intentionally not reduced to one disputed explanation.
أُقْسِمُ — I swear
Grammar: A Form IV first-person singular imperfect with understood أَنَا as subject; بِٱلشَّفَقِ is linked to it.
بِٱلشَّفَقِ — by the twilight glow
Grammar: بِ is a preposition, ٱل the definite article, and شَّفَقِ its genitive noun; the phrase is linked to أُقْسِمُ.