Word by Word Analysis

وَلَقَدْ نَعْلَمُ أَنَّهُمْ يَقُولُونَ إِنَّمَا يُعَلِّمُهُۥ بَشَرٌ ۗ لِّسَانُ ٱلَّذِى يُلْحِدُونَ إِلَيْهِ أَعْجَمِىٌّ وَهَـٰذَا لِسَانٌ عَرَبِىٌّ مُّبِينٌ 103

And We certainly know that they say, "It is only a human being who teaches him [i.e., the Prophet (ﷺ)]." The tongue of the one they refer to is foreign, and this [recitation, i.e., Qur’ān] is [in] a clear Arabic language.