So you have the capacity to scrutinize the hearts in order to determine whether a person is in good or bad faith? In your example we have an explicit statement which is referred to a non-Muslim, and we know well that Islām is the truth, but this does not prove anything. Until today I have never met an Orientalist who knows the Qur’ān by heart, and which is able to refute any Muslim; a child between monotheists could easily refute a university professor among the pagans because of his knowledge of the monotheism and the Qur’ān. It is said in Arabic, “who does not possess [something] cannot give it [to others]”. It is essential that the person who preaches the truth know what it means before preaching it to others. Aristotelians said, “the man who knows is the one who can teach others.” And we know that who reject the truth can only be ignorant of the truth and cannot prevail over those who affirm the truth, even if they have accumulated a lot of knowledge. They are included in the statement of the Exalted, “like donkeys carrying volumes [of books].” (Rough translation of the meaning of the Noble Qur'ān, 62:5) As it is said in Arabic, "The truth shines and falsity stutters". And from Allāh comes success.