How can one reconcile the innate disposition (fitra) toward Islam with God's creation of people with differences in schools of thought and beliefs?

All human beings are born upon fitra (primordial nature), which is the predisposition to accept Islam and the true religion. If a person were left to this fitra, they would remain Muslim. However, the fact that people are born upon fitra does not mean that they will all be Muslims. Indeed, Allah Almighty willed them to be diverse in religions and schools of thought, as He states: "And if your Lord had willed, He would have made mankind one nation; but they continue to differ Except those on whom your Lord has bestowed mercy."