Simplify the following text for a Grade 9 native English-speaking person.
Original: ` Abdu ` l-Bah Ã 's Will and Testament is considered one of the three charters of the BahÃ ' Ã administrative order , and in it ` Abdu ` l-Bah Ã laid down the authority of the Guardian and the Universal House of Justice , the elected governing body of the BahÃ ' Ã Faith that had been written about by BahÃ ` u 'll Ã h , and had not yet been established :
Simplified: After BahÃ ` u 'll Ã h died , Shoghi Effendi 's grandfather , ` Abdu ` l-Bah Ã lead the BahÃ ' Ã s. ` Abdu ` l-Bah Ã died , he left a `` will and testament '' that said that Shoghi Effendi was the `` Guardian '' , and that his job was to guard and lead the BahÃ ' Ã Faith . ` Abdu ` l-Bah Ã 's will said that only Shoghi Effendi could interpret ` Abdu ` l-Bah Ã 's or BahÃ ` u 'll Ã h 's books and letters .