(Extract form the article of Joel Bray Marangella, the Third Guardian of the Bahá'í Faith)
The distinguishing feature of the Revelation of Bahá'u'lláh is the binding Covenant He made with His followers to turn to 'Abdu'l-Bahá, His eldest son, after His Ascension as his appointed Successor, the sole Interpreter of His Word, the Expounder of His Book, and the Center of His Covenant; that is: the sole Center to whom all Bahá'ís should turn for spiritual guidance and interpretation of His Holy Writ. This Covenant of Bahá'u'lláh was made in a written Will and Testament which was opened on the ninth day following His Ascension in the presence of nine witnesses and read to His followers assembled in His Holy Tomb. Bahá'u'lláh has described this firm Testament as "The Book of My Covenant" (Kitáb-i-'Ahd) and "His Most Great Tablet". He has further extolled this mighty Covenant as the "Conclusive Testimony", the "Universal Balance", the "Magnet of God's grace", the "Upraised Standard", the "Irrefutable Testament", the "almighty Covenant, the like of which the sacred Dispensations of the past have never witnessed", and "one of the distinctive features of this most mighty cycle”.
It will suffice for our purpose to quote the following excerpt from Bahá'u'lláh's Testament as evidence of the uniqueness and strength of His Covenant with His followers:
"It is incumbent upon the Aghsan (His sons), the Afnán (kindred of the Báb) and My kindred to turn, one and all, their faces toward the Most Mighty Branch. Consider that which We have revealed in Our Most Holy Book (Kitáb-i-Aqdas): 'When the ocean of My presence hath ebbed and the Book of My Revelation is ended, turn your faces toward Him Whom God hath purposed, Who hath branched from this Ancient Root.' The object of this sacred verse is none other except the Most Mighty Branch ('Abdu'l-Bahá). Thus have we graciously revealed unto you our potent Will, and I am verily the Gracious, the All-Powerful".
Further corroboration of Bahá'u'lláh's appointment of 'Abdu'l-Bahá as His successor is contained in His Most Holy Book wherein He proclaims:
"When the Mystic Dove will have winged its flight from its Sanctuary of Praise and sought its far-off goal, its hidden habitation, refer whatsoever ye understand not in the Book, to Him ('Abdu'l-Bahá) Who hath branched from this mighty Stock."
In an address given by 'Abdu'l-Bahá in New York City during His visit to America in 1912 His statements concerning His appointment as the Center of His Father's Covenant included the following:
"As to the most great characteristic of the revelation of Bahá'u'lláh, a specific teaching not given by any of the prophets of the past, it is the ordination and appointment of the Center of the Covenant. By this appointment and provision He has safeguarded and protected the religion of God against differences and schisms, making it impossible for any one to create a new sect or faction of belief. To insure unity and agreement He has entered into a Covenant with all the people of the world including the interpreter and explainer of His teachings so that no one may interpret or explain the religion of God according to his own view or opinion and thus create a sect founded upon his individual understanding of the divine words."
In spite of the firmness and clarity of Bahá'u'lláh's testamentary instructions concerning the appointment and authority of 'Abdu'l-Bahá (accepted by the Heterodox Bahá'ís, too), following the Ascension of Bahá'u'lláh these instructions were flagrantly violated as 'Abdu'l-Bahá had to contend with betrayal, treachery and infidelity within the ranks of most of those who had been the closest to Bahá'u'lláh.
As time went on, however, the faithful rallied to the support of 'Abdu'l-Bahá, and it became increasingly clear that only through the providential provisions of Bahá'u'lláh's Covenant appointing a Center to whom all Bahá'ís could turn following His Ascension and vesting in Him sole authority for interpretation of His Holy Writ had Bahá'u'lláh protected and safeguarded His teachings from corruption – a protection that could only continue to be vouchsafed to it down through the ages to come of His Dispensation if the same Center provided in His unique Covenant were perpetuated for as long as this Dispensation endured. For as 'Abdu'l-Bahá stated:
"Were it not for the protecting power of the Covenant to guard the impregnable fort of the Cause of God, there would arise among the Bahá'ís, in one day, a thousand different sects as was the case in former ages..."
The uninterrupted continuity of a Center to whom all Bahá'ís were enjoined to turn following His passing was provided by 'Abdu'l-Bahá in a Will and Testament written in His own hand. This Document did far more than appoint an immediate successor to serve as the Center of the Cause. 'Abdu'l-Bahá established an Institution – the Institution of the guardianship of the Cause of God in which a "Center of the Cause" and an unchallengeable and continuing source of interpretative authority would be preserved down through the centuries to come of the Dispensation of Bahá'u'lláh. His Will and Testament called for the Institution of the guardianship to be occupied by a continuous and unbroken succession of Guardians each of whom would be chosen and appointed by the predecessor-Guardian "in his own life-time" (i.e. not designated by testamentary document). As the first occupant of this supreme Office 'Abdu'l-Bahá appointed His eldest grandson (i.e. a "twig" and not a "Branch" of His Family Tree). More than this 'Abdu'l-Bahá in His Will and Testament delineated the other institutions of the Bahá'í Administrative Order and this momentous Document constituted the Charter of the World Order of Bahá'u'lláh. The other administrative institutions incorporated in this Charter included the International (or Universal) House of Justice – the supreme legislative institution of this Order, the institution of the Hands of the Cause and the National and Local Houses of Justice. All of these institutions were made subordinate to the Guardian of the Cause as 'Abdu'l-Bahá's Will included the clear injunction:
"The mighty stronghold shall remain impregnable and safe through obedience to him who is the guardian of the Cause of God."