And their number we have made only a trial for those who disbelieve , so that those who are vouchsafed the Book may be convinced , and that those who believe may increase in faith , and that those who are vouchsafed the Book and the believers may not doubt , and that those in whose hearts is a disease and the infidels may say : what meaneth Allah by this description ! In this wise Allah sendeth astray whomsoever He will , and guideth whomsoever He will .