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Surah 2. Al-Baqara
Ayah 135 - 136
135وَقَالُوا۟ كُونُوا۟ هُودًا أَوْ نَصَـٰرَىٰ تَهْتَدُوا۟ ۗ قُلْ بَلْ مِلَّةَ إِبْرَٰهِـۧمَ حَنِيفًا ۖ وَمَا كَانَ مِنَ ٱلْمُشْرِكِينَ
136قُولُوٓا۟ ءَامَنَّا بِٱللَّهِ وَمَآ أُنزِلَ إِلَيْنَا وَمَآ أُنزِلَ إِلَىٰٓ إِبْرَٰهِـۧمَ وَإِسْمَـٰعِيلَ وَإِسْحَـٰقَ وَيَعْقُوبَ وَٱلْأَسْبَاطِ وَمَآ أُوتِىَ مُوسَىٰ وَعِيسَىٰ وَمَآ أُوتِىَ ٱلنَّبِيُّونَ مِن رَّبِّهِمْ لَا نُفَرِّقُ بَيْنَ أَحَدٍ مِّنْهُمْ وَنَحْنُ لَهُۥ مُسْلِمُونَ
[135-136] The Jews say, "Become Jews and you will be rightly guided" ;the Christians say, "Become Christians and you will have the true guidance." Say to them, "Nay, we turn away from every other way and accept the way of Abraham, and Abraham did not associate other gods with Allah."135 O Muslims, say to them, "We believe in Allah and the Guidance which has been sent down to us and which was sent to Abraham, Ismail , Isaac and Jacob and his descendants and which was given by their Lord to Moses and Jesus and to all other Prophets. We do not discriminate against any of them136 and we have completely surrendered to Allah as Muslims."
135In order to understand the true significance of this answer, two things should be kept in mind.
(1) Judaism and Christianity were born long after the death of Abraham. Judaism, with its special rituals, peculiar regulations, etc., took its birth and name some tour hundred years before Christ. As to "Christianity", it took its name and adopted its special creed and form long after the recall of Jesus. Thus it is clear that their claim that one must become a Jew or a Christian in order to obtain guidance was historically untenable. For in that case, Abraham, Jesus and all the other Prophets and all the good people who had passed away long before the birth of Judaism and Christianity could not be counted among the right-guided persons for the simple reason that these "religions" did not exist at the time they lived. Thus, it was obvious that the Jews and Christians could not say that these Prophets were not right-guided, nor could they claim that they followed Judaism or Christianity. As a corollary to this, true Guidance did not, even according to them, consist of the particular features which divided them into two distinct religions, but it was that eternal universal way which has been shown by all the Messengers of Allah and which has always been followed by the good people of all ages.
(2) It also meant to warn the Jews and the Christians that both practised shirk and had, therefore, swerved from the way of Abraham, who did not associate any other object with Allah in his worship, his reverence, his submission and his obedience to Him. They could not deny this because their own Scriptures bore testimony to it.
136"We do not discriminate against any of them" means that we believe in all the Prophets of Allah and reject none. It is obvious that all the Prophets who came from Allah brought the same Truth and invited the people to the same Guidance and Right Way. Hence anyone who follows the Truth must accept all the Prophets. Those who accept one Prophet and reject the other really reject even the one whom they profess to accept. Had they followed the universal Guidance taught by Moses, Jesus and other Prophets, they could not have rejected any other Prophet (i.e. Muhammad, Allah's peace be upon him). As a matter of fact, they were not following the teachings of any Prophet, but merely professing to accept their own Prophets just because their fathers did so. Thus their real religion was prejudice, race-worship and blind imitation of their forefathers.