Tafsir of Al Imran 3:66

Then, He—Glory be to Him—alerted them to their foolishness by saying: "Lo! You are those..." meaning: You are those fools "who have argued about that of which you have some knowledge"—such as the matter of Moses and Jesus, peace be upon them—"so why do you argue about that of which you have no knowledge?"—which is the matter of Abraham, peace be upon him, as there is no mention of his religion in your scripture, nor is there any reference to the fact that he believed in Moses and Jesus prior to their mission at all.

It is not intended to describe them as possessing true knowledge; rather, the intent is: "Suppose you argue about what you claim to have knowledge of, based on what appears to you through the phrasing and allusions of your scripture in your own estimation, how then do you argue about that of which you have no knowledge, no mention, and no symbol in your scripture whatsoever?"

"Ha" is a particle of attention. It is customary for it to precede a subject when its predicate is a demonstrative noun, such as "Ha ana dhu" (Lo! I am here). It is repeated here for emphasis. Al-Akhfash held that the origin was "A-antum" (Are you?), as an interrogation, where the hamzah was changed into a ha'. To him, the meaning of the interrogation is astonishment at their ignorance. Abu Hayyan critiqued this, saying it is not sound, because it was not heard in their speech that the interrogative hamzah is replaced by a ha' except in a rare poetic verse. Furthermore, separating the replaced ha' and the hamzah of "antum" is inappropriate, because separation is only done to avoid the heaviness of two consecutive hamzahs, and here that heaviness is already removed by replacing the first with a ha'. The demonstrative is used for disparagement and belittlement, from which is understood the description that clarifies the purpose of the predication.

The sentence "you have argued" is a new, explanatory sentence for the first. It is also said that it is a circumstantial (hal) clause, evidenced by the fact that the circumstantial clause often occupies its place, as in "Ha ana dhu qa'iman" (Lo! I am here, standing), and this state is essential. It is also said that the sentence is the predicate of "antum," and "ha'ula'" is a vocative from which the vocative particle has been omitted. It is also said that "ha'ula'" means "those who," being the predicate of the subject, and the sentence "you have argued" is the relative clause (silah); the Kufans held this view. Their readers recite "Ha antum" with prolongation (madd) and a hamzah. The people of Medina and Abu ‘Amr recited it without hamzah or prolongation, except to the extent of uttering the silent alif. Ibn Kathir and Ya‘qub recited it with hamzah and shortening (qasr) without prolongation. Ibn ‘Amir recited it with prolongation without hamzah.

"And Allah knows..." the state of Abraham and what he was upon, "while you do not know" that. You may consider the object to be general, and what is mentioned is included therein primarily. The sentence is an affirmation of their lack of knowledge regarding the matter of Abraham, peace be upon him.