We have appointed only angels to be masters of the Fire , and their number We have appointed only as a trial for the unbelievers , that those who were given the Book may have certainty , and that those who believe may increase in belief , and that those who were given the Book and those who believe may not be in-doubt , and that those in whose hearts there is sickness , and the unbelievers , may say , ' What did God intend by this as a similitude ? ' So God leads astray whomsoever He will , and He guides whomsoever He will ; and none knows the hosts of thy Lord but He .