16.103 – Only a human being teaches him
The third challenge is an accusation from the audience that the messenger has simply learned his preaching from someone else (see also 25:4–5). No name is given for the alleged teacher, so Muslim commentaries on the Quran supplied a number of names to identify the teacher, including a Christian slave. The Quran’s response, however, is that the teacher the audience is thinking of speaks a foreign language.
Readers who would like a taste of traditional Muslim interpretation in translation can see the commentary of Zamakhsharī (d. 1144) on this verse in Helmut Gätje’s The Qur ’ án and its Exegesis.

16.103 – this language is clear Arabic
The Quran seems to put forward, as a kind of proof, that the messenger could not be preaching what another has taught him because his recitation is in Arabic. The assertion is that the recitations must be “sent down.” See the analysis of claims for “Arabic” at 43.2–3.