Mankind were one community. (Nature's provision was abundant and open for all (2:36). Then Satan, their selfish desire, divided them (10:19)) Allah sent Prophets as heralds of good news and as Warners. He sent down with them the Scripture with the Truth to judge among people in their differences. After the Prophet passed on, people started differing in the Scripture that was given to them with clear verses. And they did so in stubborn rivalry. Allah by His Will keeps the sincere believers guided in Truth concerning whatever differences arise among them. Allah guides people according to His Laws. (Using your faculties of listening, observing and reasoning will help you achieve guidance, while selfishness, arrogance and blind following will lead people astray (2:170), (6:56), (40:35), (41:17)).