Wama tafarraqa allatheena ootoo alkitaba illa min baAAdi ma jaat-humu albayyina (surah Bayyinah: 4)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(98:4) Nor did those to whom the Book had been given split up until after the Proof (of the Right Way) had come to them. *6

Wa maa tafarraqal lazeena ootul kitaaba il-la mim b`adi ma jaa-at humul baiyyinah

*6) That is, the reason why the people of the Book before this were divided into countless sects because of different kinds of errors and deviation, was not that Allah had failed to send "a clear evidence" from Himself for their guidance, but the fact that they adopted the wrong way after guidance had come from Allah; therefore, they themselves were responsible for their deviation, for Allah had fulfilled His obligation towards them. Likewise, since their scriptures are no longer pure and their books no longer consist of original and correct teachings, Allah by sending a Messenger of His, as a clear evidence, with a hallowed Book, containing sound and pure teachings, has again fulfilled His obligation towards them, so that if even after that they remained divided, they themselves should be responsible for it and should have no excuse left to plead before Allah. This thing has been stated at many places in the Qur'an, e.g. see AI-Baqarah: 213, 253; AI-`Imran: 19: Al-Ma'idah: 44-50; Yunus: 93; Ash-Shura: 13-I5; Al-Jathiyah: 16-18, along with the corresponding notes for fuller understanding.