Tafsir of Nuh 71:2

"He said" is an explanatory resumption, as if it were said: "What did he—upon him be prayer and peace—do after this mission?" It is said: He said to them, "O my people, indeed I am to you a clear warner." [That is,] a warner who clarifies the reality of the matter. The lam in "to you" (lakum) is for intensification or for indicating the cause; meaning: for the sake of your benefit, without me asking you for any reward.

And His saying, the Exalted...