Grand jurors shall, before they begin performance of their duties, solemnly swear or affirm that they will diligently inquire as to all matters and things which come before the grand jury; that they will keep all matters which come before the grand jury secret; that they will indict no person for envy, hatred or malice; that they will not leave any person unindicted for love, fear, favor, affection or hope of reward; and that they will indict truly, according to the best of their understanding.