 Bahá 'u'lláh 's Kitáb @-@ i @-@ Aqdas and The Will and Testament of `Abdu 'l @-@ Bahá are foundational documents of the Bahá 'í administrative order . Bahá 'u'lláh established the elected Universal House of Justice , and `Abdu 'l @-@ Bahá established the appointed hereditary Guardianship and clarified the relationship between the two institutions . In his Will , `Abdu 'l @-@ Bahá appointed his eldest grandson , Shoghi Effendi , as the first Guardian of the Bahá 'í Faith , serving as head of the religion until his death , for 36 years . 
