(And We have not sent you except as a giver of glad tidings and a warner to all mankind,) i.e., to all of creation among those who are accountable for their deeds. This is like the Ayah:
That Allah is One and that His power is absolute was the subject in previous verses. In the present verse, it is being said that the Holy Prophet ﷺ “ was sent as the Messenger of Allah to all peoples of the world who are there now or will come in the future.
The word: كَافَّةً (Kaaffah) in: كَافَّةً لِلنَاس Kaaffatal-lin-naas: for all peoples) is used in the sense of making something universal and inclusive of all without the exclusion of anyone from it. The grammatical arrangement of the text required saying: لِلنَاس (lin-naasi kaaffatan: for the people as a whole) because the word: (kaaffah: all) is grammatically a hal (adverb) relatable to the word نَاس (naas: people). But, in order to put a clear accent on the universality of the mission of the Last Rasul of Allah, the word: كَافَّةً (Kaaffah: all) was set to come earlier.
The Universe is unimaginably great. Moreover, perfect wisdom and meaningfulness is inherent in it. Such a universe can be the accomplishment of the All-powerful, All-wise God alone. No one can seriously believe that those beings, whom ancient or modern man has invented can be the creators or lords of this universe. This being so, who other than God can be the one who enjoys the position of supremacy in this Universe? The fact is that the study of the universe invalidates all polytheistic theories. As such, only that theory can be correct which is based on the oneness of God. Any theory which projects the instrumentality of any being other than God is self-contradictory.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.