The Child of the Covenant
From Bahaipedia

His final book, Adib Taherzadeh's sequel to The Covenant of Bahá’u’lláh provides a detailed and insightful study of the Will and Testament of ‘Abdu’l-Bahá, the 'Charter of Bahá’u’lláh's New World Order'.
The Will and Testament of ‘Abdu’l-Bahá constitutes a fundamental document of the Covenant of Bahá’u’lláh. Described by Shoghi Effendi as 'the Child of the Covenant' the importance of its study becomes obvious when we note that Shoghi Effendi has stipulated that one of the qualifications of a true believer is 'loyal and steadfast adherence to every clause of our Beloved's sacred Will'.
Full Title[edit]
The Child of the Covenant: A Study Guide to the Will and Testament of ‘Abdu’l-Bahá
Author[edit]
Publisher[edit]
ISBN[edit]
978-0-85398-439-5