Indeed, the religion in the sight of Allah is Islam. And those who were given the Scripture did not differ except after knowledge had come to them - out of jealous animosity between themselves
إن الدين عند الله الإسلام وما اختلف الذين أوتوا الكتاب إلا من بعد ما جاءهم العلم بغيا بينهم [Ali 'Imran 3:19]
This means that this Ummah agreed upon Islam and did not differ in it, but the previous nations experienced difference among them. Nevertheless, they did not differ except after knowledge had come to them and they knew the truth, yet they differed in it out of transgression and arrogance, each one of them transgressing against the other, each one of them saying that your religion is invalid, so they split and tore apart. This, as it was found in the previous nations, was found in this Ummah; we find some scholars contradicting others, then they turn this disagreement into a disagreement of the heart, so the hearts become hostile and scattered. Whoever is in that state has a resemblance to whom? To the Jews and the Christians. And His saying:
after knowledge had come to them
من بعد ما جاءهم العلم [Ali 'Imran 3:19]
Knowledge of what? Knowledge of the Shari'ah. After they knew the Shari'ah and learned it, they disputed over it. And His saying:
out of envy, among themselves
بغيا بينهم
means that what drove them to this difference was transgression, that some of them transgressed against others, and for this reason it occurred between the Jews and the Christians