The second verse (91) has been revealed in answer to those who had the audacity to say that Allah Ta` ala has just not revealed any book to any human being. According to them, this whole proposition of books and messengers was all wrong.

If, those who said that are the idolaters of Makkah, as mentioned by Ibn Kathir, then, the matter is obvious, for they did not believe in any book and prophet. And if they were Jews, as held by other commentators - and the contextual elements of the verse obviously support this view - then, their saying so was an outcome of their anger and irritation, something contrary to the dictates of their own religion. According to a narration of Imam al-Baghawi, this was the reason why the Jews too were displeased with the person who had made this unfortunate remark, and it was because of this erroneous conduct of his that he was removed from his office of religious authority.

In this verse, Allah Ta` ala has said to the Holy Prophet ﷺ that people who made this absurd remark did not recognize the Most True Allah as was His right to be recognized. Had they done that, this audacious remark would have never escaped their lips. Then, Allah Ta` ala tells the Holy Prophet ﷺ to ask the people who deny Scriptures absolutely: If that is what you think - that Allah Ta` ala did not reveal any book to any human being - then, you better have an answer as to who revealed the Torah, in which you too believe, and because of which you sit in judgment over your people. Along with it, they were also told: You are such connoisseurs of crooked ways that you would treat your own book, the Torah, which you believe in as being Holy Scripture, in a way that you got it conveniently written on separate sheets, rather than having it in a formally bound book, so that you can take out any sheet from it as and when you want it, and by doing so you would have the option of denying what it enjoined. An example of this are the verses of the Torah which described the signs and attributes of the Messenger of Allah which you have excluded. The last sentence of the verse: تَجْعَلُونَهُ قَرَ‌اطِيسَ (which you kept in sheets) means exactly this. The word: قَرَ‌اطِيسَ (qaratis) is the plural of: قِرطَاس (qirtas) which means sheet or paper.

After that, addressing the same people, it has been said: وَعُلِّمْتُم مَّا لَمْ تَعْلَمُوا أَنتُمْ وَلَا آبَاؤُكُمْ that is, you were taught (through the Qur an) what you or your forefathers did not know (earlier, either through the Torah or the Injil).

At the end of verse (91), it was said: قُلِ اللَّـهُ ۖ ثُمَّ ذَرْ‌هُمْ فِي خَوْضِهِمْ يَلْعَبُونَ (Say, "Allah." Then leave them playing with what they are indulged in). In other words, the sense is: As for the question - if Allah just did not send any book, who sent the Torah? - it was something they would not know how to answer, so, you go ahead and tell them that it was revealed by none but Allah. Now that the argument against them stands concluded, your mission as far as they are concerned is over. So, let them be lost in the game they are playing.