Al-Hajj: (17) Indeed, those who have believed...
"He will judge between them"
The separation is absolute, encompassing all states and places. Thus, He will not recompense them with a single, undifferentiated reward, nor will He gather them in one place.
It is said: The religions are five—four for Satan and one for the Most Merciful. The Sabians were grouped with the Christians because they are a sect of them.
It is also said: "He will judge between them" means He will pass judgment between them, that is, between the believers and the disbelievers.
The particle "Indeed" (Inna) was introduced into both parts of the sentence—"Indeed, those who have believed... [and] indeed, Allah will judge between them"—for the sake of emphatic reinforcement. Similar to this is the verse of Jarir:
Indeed, the Caliph—indeed, Allah has clothed him
In the garment of kingship, through which good endings are hoped for.
"Do you not see that to Allah prostrates whoever is in the heavens and whoever is on the earth, and the sun, the moon, the stars, the mountains, the trees, the moving creatures, and many of the people? But for many, the punishment has been justified. And he whom Allah humiliates—for him there is no bestower of honor. Indeed, Allah does what He wills."