The text drops its majestic divine tone to frantically answer local Meccan critics, revealing a deep contemporary doubt regarding the text's origin.
Surah 69:41-43:
And it is not the word of a poet; little do you believe. Nor the word of a soothsayer; little do you remember. [It is] a revelation from the Lord of the worlds.
The Meccans accused Muhammad of being a "poet" (sha'ir) and a "soothsayer" (kahin) because the stylistic formatting of the early Meccan Surahs—including Surah 69 itself—perfectly matched the style of Saj'.
Saj' was a highly distinct form of rhymed, rhythmic prose used exclusively by pagan Arab fortunetellers and occultists of that era when delivering their rhyming incantations.
Because the Quran sounded exactly like the pagan occultists of the day, the Meccans naturally categorized it as such.
Instead of proving its divinity through a uniquely distinct supernatural style, the text relies on a flat, defensive denial. It mimics human literature and then demands belief simply because it claims to be from the "Lord of the worlds."
An eternal, self-evidently divine book does not need to pause its decrees to tell local hecklers, "I am not a poet, I am not a fortuneteller."
The inclusion of these anxious denials within the text itself shows that the Quran was reacting in real-time to the very valid suspicions of Muhammad's peers who recognized the text as matching the style of contemporary rhymed prose (Saj').