The genitive construction of “witnesses” and the pronominal suffix “your (-kum)” denotes particularity and strengthens the first meaning [above]: “Your great ones are present with you and there are special [bonds] between you; if they had been capable of helping you, surely [they would have done].” It expresses the second meaning like this: “We accept the testimony of those who support you and are your partisans, for they won’t venture to testify for something whose invalidity is self-evident.” And it takes the third meaning by the arm and mocks it, saying: “Why don’t the gods you worship help you?”
With respect to the first, the phrase “besides Allah (min dūn Allāh)” indicates generality; that is, [call] all the eloquent masters of language in the world other than Allah the Most High. It indicates too that [the Qur’an’s] miraculousness is only [miraculousness] because it is from Allah.
With respect to the second, it indicates their impotence and confusion when they say: “Allah is our witness. Allah knows that we can do it.” For it is the habit of those defeated in argument and reduced to impotence to swear by Allah and call on Him to witness what they are incapable of proving.
And with respect to the third it indicates that their disputing the Messenger (Upon whom be blessings and peace) was exactly the response of associating partners with Allah (shirk) to divine unity (tawḥīd), and of lifeless, unconscious beings to the Creator of the heavens and the earth.
The phrase “if what you say is true (in kuntum ṣādiqên)” alludes to their saying: “If we wanted, we could say something similar.” It also insinuates: “You aren’t truthful. Your truthfulness is only hypothetical; indeed, you only utter sophistries. And you haven’t fallen into doubt because you were seeking the truth, but because you were seeking the false, and you fell into it. Furthermore, the consequence (apodosis) [of the conditional verb “if what you say”] is the sum and substance of the previous phrases; that is, “do it!” That is, “If what you say is true, then try to produce something similar.”
The sentence: “But if you cannot, and of a surety you cannot, then fear the Fire (Fa-in lam taf‘alū wa lan taf‘alū fa-‘ttaqū al-nār):” with the phrase “If what you say is true” the Qur’an is confuting them with a conditional syllogism, excepting the opposite of the following phrase to occasion the opposite of the preceding one.
A summary of it: “If you were truthful, you would have disputed it and produced a sura, but you didn’t [coundn’t] and you won’t [be able to]. One