And He it is Who made you successors of the earth, and raised the grades of some of you above others that He may test you through that which He has given you. Your Fosterer is certainly Quick in requiting while He is (also) Protectively Forgiving, Merciful. (R 20, P 7
Allah (SWT) has made mankind successors (i.e. incharge of certain affairs) of this world creating among them economic, social, political, religious differences to test them as to who is grateful in success and who is patient in adversities.