Why was "لا" (la) added in His, the Almighty's, saying: "لا أقسم بهذا البلد" (la uqsimu bihadha al-balad), and is it permissible for "لا" here to be for negation?

The exegetes differed regarding the meaning of the negation with "la" in His (the Most High) saying: (فَلاَ أُقْسِمُ بِمَوَاقِعِ النُّجُومِ - So I swear by the places of the stars). The most probable opinion is that "la" is an extra particle for emphasis, and the meaning is: "So I swear." This is indicated by His (the Most High) saying: (وَإِنَّهُ لَقَسَمٌ - And indeed, it is a great oath). This is what the majority of exegetes adopted, and Al-Zamakhshari affirmed it, citing poetic examples. Al-Qurtubi mentioned that Abu Al-Layth Al-Samarqandi narrated the consensus of the exegetes that the meaning is: "I swear."