Tafsir of Al-Anbiya' 21:8

{They did not eat food} This is an adjective describing "a body" (jasadan). The meaning is: We did not make the prophets—peace be upon them—before him possessors of a body that does not eat food. The word "body" is singular to denote the genus (category), as if He said: "possessors of a type of body." This is a refutation of their saying: {Why does this messenger eat food?} (Al-Furqan: 7).

If you ask: Yes, their denial that a messenger could be a human who eats and drinks has been refuted by what you mentioned, but what is being refuted by His saying: {And they were not immortal}?

I say: It is possible they were saying: "He is a human like us, living as we live and dying as we die." Or they were saying: "Why is he not an angel who does not eat and is immortal?" This is either because they believed angels do not die, or because they termed their prolonged lives and extended existence as "immortality."

{Then We fulfilled the promise to them, and We saved them and whom We willed, and We destroyed the transgressors.}