We have appointed only angels to be wardens of the Fire , and their number have We made to be a stumbling-block for those who disbelieve ; that those to whom the Scripture hath been given may have certainty , and that believers may increase in faith ; and that those to whom the Scripture hath been given and believers may not doubt ; and that those in whose hearts there is disease , and disbelievers , may say : What meaneth Allah by this similitude ? Thus Allah sendeth astray whom He will , and whom He will He guideth .