And it is well known that he was among the most eloquent of people and the clearest in expression. The language in which he addressed them was the most complete of languages and the fullest in its expressive power. Allah reminded them of this favor, as in His words, Most High:

“Alif, Lām, Rā. These are the verses of the clear Book. Indeed, We have sent it down as an Arabic Quran so that you may understand.”
[Yūsuf: 1–2].

And He, Most High, says:

“Indeed, We have made it an Arabic Quran so that you may understand.”
[Al-Zukhruf: 3].

And He, Most High, says:

“We have not sent any messenger except in the language of his people, so that he might make things clear to them.”
[Ibrāhīm: 4].

And He, Most High, says:

“The Trustworthy Spirit has brought it down upon your heart, so that you may be one of the warners, in a clear Arabic language.”
[Al-Shu'arā': 193–195].

And He, Most High, says:

“The language of the one to whom they allude is foreign, while this is a clear Arabic language.”
[Al-Nahl: 103].

There are other passages to the same effect.

Thus, if the speaker is the most knowledgeable of all creation about what he speaks of, describes, and reports; the most eager of all creation to make his listeners understand, inform them, teach them, and guide them; and the most capable of all creation of clearly explaining his intended meaning and purpose, then it is necessarily impossible for his words not to convey knowledge, guidance, and truth concerning what he addresses, reports, explains, and describes. Rather, his words must be the words most deserving of being recognized as conveying knowledge, truth, and guidance, while any words that contradict his must be the words most deserving of being regarded as ignorance, lies, and falsehood.