Abbas - Tanwîr al-Miqbâs min Tafsîr Ibn ‘Abbâs
(Lest ye should say) so that you will not say, O people of Mecca, on the Day of Judgement: (The Scripture was revealed only to two sects) the people of two religions (before us) i.e. the Jews and Christians, (and we in sooth were unaware) ignorant (of what they read) their reading of the Torah and the Gospel;
We have revealed it, lest you should say, ‘The Scripture was revealed only upon two parties — the Jews and the Christians — before us and we (in has been softened, its noun omitted, in other words [read as] innā) indeed have been unacquainted with their study’, their reading [of the scripture], not knowing any of it, since it is not in our own language.
(Otherwise, they would have suffered a calamity because of what their hands sent forth, and said: "Our Lord! Why did You not send us a Messenger We would then have followed Your Ayat.'')28:47.'' The Ayah,
عَلَى طَآئِفَتَيْنِ مِن قَبْلِنَا
(to two sects before us) refers to the Jews and Christians, according to `Ali bin Abi Talhah who narrated it from Ibn `Abbas. Similar was reported from Mujahid, As-Suddi, Qatadah and several others. Allah's statement,
وَإِن كُنَّا عَن دِرَاسَتِهِمْ لَغَـفِلِينَ
("...and for our part, we were in fact unaware of what they studied.") meaning: `we did not understand what they said because the revelation was not in our tongue. We, indeed, were busy and unaware of their message,' so they said. Allah said next,
(Or lest you should say: "If only the Book had been sent down to us, we would surely, have been better guided than they.") meaning: We also refuted this excuse, had you used it, lest you say, "If a Book was revealed to us, just as they received a Book, we would have been better guided than they are.'' Allah also said.
(So now has come unto you a clear proof from your Lord, and a guidance and a mercy.) Allah says, there has come to you from Allah a Glorious Qur'an revealed to Muhammad, the Arab Prophet. In it is the explanation of the lawful and unlawful matters, guidance for the hearts and mercy from Allah to His servants who follow and implement it. Allah said;
(Who then does more wrong than one who rejects the Ayat of Allah and Sadafa away therefrom) This refers to the one who neither benefited from what the Messenger brought, nor followed what he was sent with by abandoning all other ways. Rather, he Sadafa from following the Ayat of Allah, meaning, he discouraged and hindered people from following it. This is the explanation of As-Suddi for Sadafa, while Ibn `Abbas, Mujahid and Qatadah said that Sadafa means, he turned away from it.
Maududi - Sayyid Abul Ala Maududi - Tafhim al-Qur'an
That is, to the Jews and the Christians.
Here "Ayat" are Allah's Revelations presented in the Holy Qur'an as well as His Messenger's noble character and the pure lives of the Believers which clearly distinguished them from the unbelievers, and also those wonderful phenomena of Nature which the Qur'an was putting forward as proofs of the truth of its Message.
"Manifest Signs" are the signs of the Day of Resurrection or some imminent scourge or some other Sign that tray unveil the Reality in such a way as to leave no doubt about it and after which no more chance for test and trial might be left.
That is, if after seeing these "Manifest Signs" a disbeliever repents of his disbelief and professes faith, such a conversion shall be meaningless; likewise the one who professes to believe but adopts the way of disobedience, shall be deemed to have no faith at all, because Faith and Obedience can have any value only up to the time that the reality remains hidden behind the curtain, and the prospect of a long life is ahead and the world with all its allurements is deluding one into believing that there is no Allah and no Hereafter; therefore, one should "Eat, drink and be merry."