١٩. وَمَا كَانَ ٱلنَّاسُ إِلَّآ أُمَّةً وَٰحِدَةً فَٱخْتَلَفُوا۟ ۚ وَلَوْلَا كَلِمَةٌ سَبَقَتْ مِن رَّبِّكَ لَقُضِىَ بَيْنَهُمْ فِيمَا فِيهِ يَخْتَلِفُونَ
[19] In the beginning all the people were one community, but afterwards they invented different creeds and ways.25 And had not your Lord ordained a decree, that thing in which they differ would have been resolved.26
25Please see E.N. 230 of Al-Baqarah and E.N. 24 of Al- An`am.
26The "decree" that. Allah has ordained is that "the Reality" shall be kept hidden from man's senses in order to test whether he recognizes this by using his common-sense, intelligence, conscience and intuition, and if he does not, he shall be allowed to tread the wrong ways he chooses. That is why their differences about the Reality are not being resolved by uncovering it today.
This thing has been stated here to remove a common misunderstanding about the diversity of religions in the world.
At that time, there was a confusion in the minds of the people (and is even today) concerning this. They said, "Different people profess different religions, and the followers of each religion claim that their religion alone is the true one. How may then a seeker after truth judge which one of these is the true religion?" The answer is: "In the beginning all mankind had one religion only, and that was the true religion. Then people strayed away from it and invented different religions of their own with different creeds and ways. Now if you desire that Allah Himself should uncover the Truth and present it to you to enable you to decide which religion is the true one, you should know that this will not be done in this life, because you arc required to decide this by using your commonsense and intelligence. This worldly lift is a trial to sec whether or not you yourselves recognize the Truth by using your common-sense and intelligence."