Simplify the following text for a Grade 9 native English-speaking person.
Original: ` 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 . This was to prevent different people from splitting the religion up because they thought BahÃ ` u 'll Ã h or ` Abdu ` l-Bah Ã meant different things , the way many other religions have split up .
Simplified: Other branches of BahÃ ` u 'll Ã h 's family had already been declared Covenant-breakers in ` Abdu ` l-Bah Ã 's Will and Testament .