 `Abbás Effendi was Bahá 'u'lláh 's eldest son , known by the title of `Abdu 'l @-@ Bahá ( Servant of Bahá ) . His father left a Will that appointed `Abdu 'l @-@ Bahá as the leader of the Bahá 'í community , and designated him as the " Centre of the Covenant " , " Head of the Faith " , and the sole authoritative interpreter of Bahá 'u'lláh 's writings . `Abdu 'l @-@ Bahá had shared his father 's long exile and imprisonment , which continued until `Abdu 'l @-@ Bahá 's own release as a result of the Young Turk Revolution in 1908 . Following his release he led a life of travelling , speaking , teaching , and maintaining correspondence with communities of believers and individuals , expounding the principles of the Bahá 'í Faith . 
