And mankind was not but one community [united in religion], but [then] they differed. And if not for a word1 that preceded from your Lord, it would have been judged between them [immediately] concerning that over which they differ.
Translation: Saheeh International (English)
1 Allāh's decree to allow time on earth for His creation or not to punish anyone before evidence has come to him.
لَقُضِيَsurely, it (would) have been judgedlaquḍiya
بَيۡنَهُمۡbetween thembaynahum
فِيمَاconcerning whatfīmā
فِيهِ[therein]fīhi
يَخۡتَلِفُونَthey differyakhtalifūna
Tafsir
People were just one believing, unified nation, then they differed: some of them still had faith, while others disbelieved. If it had not been for the decree of Allah that He would not judge between them in what they differed about, then it would have been made clear which of them were guided and which of them were astray.