Tafsir of Al-Anbiya' 21:93

"And they divided their affair among themselves..."

The original form is taqatta‘tum (you divided), but the speech was shifted to the third person (ghaybah) following the method of iltifat (stylistic shift). It is as if He is lamenting what they corrupted to others, making their actions appear repulsive to them, and saying to them: "Do you not see the magnitude of what these people have committed regarding the religion of God?"

The meaning is: They made the matter of their religion into pieces among themselves, just as a group distributes and divides a thing, so that this one gets a share and that one gets a share. This is a metaphor for their disagreement regarding it, and their becoming various sects and disparate parties.

Then, He threatened them that these various sects will return to Him, for He is their Reckoner and their Rewarder.

"So whoever does of righteous deeds while he is a believer, there is no denial of his effort, and indeed We are, for him, recorders."