Tafsir of Sad 38:65

Say, "O Muhammad, to the polytheists of Mecca, I am only a warner." I have warned you of the punishment of Allah the Exalted for the polytheists. This speech is a refutation of their statement, "This is a sorcerer, a liar," for warning contradicts sorcery and lying. It may also be said: The meaning is "I am only a messenger, a warner, not a sorcerer or a liar." There is much excellence in this, for each of the two descriptions—Messengership and Warning—contradicts each of the two descriptions—Sorcery and Lying. However, the contradiction between Messengership and Sorcery is more evident, and there is an antithesis (tibaq) between them; likewise, there is an antithesis between Warning and Lying.

To this, He the Exalted added: "And there is no god but Allah," to indicate that he, peace be upon him, also possesses the quality of calling to His Oneness, Exalted and Majestic is He. Thus, the two matters independently provide the benefit.

The "min" is extraneous, used for emphasis; meaning: there is no god at all except Allah, the One—that is, He who does not admit plurality in His Essence, neither in terms of particulars, such that He, Glory be to Him, would have a universal quiddity, nor in terms of parts—the Subduer of all things.