Shoghi Effendi wrote that the Covenant of Baha'u'llah "can find no parallel in the Scriptures of any previous Dispensation," and that in none of them "do we find any single document establishing a Covenant endowed with an authority comparable to the Covenant which Bahá'u'lláh had Himself instituted." (God Passes By, p. 238)
This Covenant is described in remarkable language:
"Baha'u'llah's peerless Covenant" (Shoghi Effendi, The Promised Day is Come, p. 14)
"Baha'u'llah's peerless and all-enfolding Covenant" (Shoghi Effendi, The World Order of Baha'u'llah, p. 133)
"Baha'u'llah's incomparable Covenant" (Shoghi Effendi, Messages to America, p. 50; This Decisive Hour, paragraph 85.8)
"a Covenant of world importance, pre-existent, peerless and unique in the history of all religions." (Shoghi Effendi, God Passes By, p. 248)
"a Covenant designed by Him as the sole refuge against schism, disruption and anarchy." (Shoghi Effendi,Messages to America, p. 50; This Decisive Hour, paragraph 85.8)
"the Covenant of Baha'u'llah, a document without parallel in the history of any earlier Dispensation" (Shoghi Effendi, God Passes By, p. xv)
What is this remarkable Covenant? What does it say? In its essence it is remarkably simple and straightforward: In Baha'u'llah's own handwriting, it simply says that after His passing, the Baha'is should "turn" to Abdu'l-Baha. It does not put conditions on this, nor explanations, nor a list of powers. It does not expressly specify that Abdu'l-Baha would be infallible, though, as Abdu'l-Baha Himself explained in His Last Tablet to America, this is clearly implicit in His Covenant:
"... the Blessed Beauty (may my soul be a sacrifice unto Him), has through the Supreme Pen written the Covenant and the Testament; He appointed a Center, the Exponent of the Book and the annuller of disputes. Whatever is written or said by Him is conformable to the truth and under the protection of the Blessed Beauty. He is infallible."
The essence of the Covenant of Baha'u'llah is contained in the single word, "turn." It is expressed this way, in Baha'u'llah's Most Holy Book:
"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 Kitab-i-Aqdas, paragraph 121, p. 62)
All of these majestic adjectives--peerless, all-enfolding, incomparable, unique--all of these describe this simple phrase. None of the past Revelations has provided a written Covenant, so clear and unmistakeable in its direction.
All of the powers Abdu'l-Baha exhibited during his 29 year ministry, were authorized by that single word, "turn." Baha'u'llah did not provide a list of powers and limitations; He simply directed the Baha'is to turn to His Successor. I refer to this as the "plenary power" of Abdu'l-Baha. It is a broad and emphatic grant of authority.
In His turn, Abdu'l-Baha in the closing words of His Will and Testament, wrote the same thing; He said to turn to, and seek guidance from, the Guardian of the Cause and the Universal House of Justice: "All must seek guidance and turn unto the Center of the Cause and the House of Justice. And he that turneth unto whatsoever else is indeed in grievous error." (Abdu'l-Baha, The Will and Testament, p. 25) This, likewise, is a broad authority granted to both the Guardian of the Cause, and the Universal House of Justice.
I live in the United States, and constitutionally, the American federal government is considered to be a government of "limited powers." That is, its powers are limited to those specified in the federal constitution, which have been granted to it. Every legislative enactment, every executive act, must fit within the specific powers granted to the federal government by the states and by the individual citizens. This is in sharp contrast to the broad and unspecified powers granted through the word "turn."
In Baha'u'llah's Will, He directed His male descendants, the Aghsan (an Arabic word meaning "branches") and the Afnan (an Arabic word meaning "twigs", referring to the relatives of the Bab) to turn to Abdu'l-Baha:
"The Will of the divine Testator is this: It is incumbent upon the Aghsan, the Afnan and My Kindred to turn, one and all, their faces towards the Most Mighty Branch." (Baha'u'llah, "The Book of My Covenant," Tablets of Baha'u'llah, p. 221)
The language of Abdu'l-Baha's Will is very similar:
"After the passing away of this wronged one, it is incumbent upon the Aghsan (Branches), the Afnan (Twigs) of the Sacred Lote-Tree, the Hands (pillars) of the Cause of God and the loved ones of the Abha Beauty to turn unto Shoghi Effendi..." (Abdu'l-Baha, The Will and Testament, p. 11)
In the Will, the Guardian of the Cause and the Universal House of Justice were given specific functions. Some of these functions were shared--common to both institutions; some of these functions are unique. The Guardian was given the unique function of interpretation of the revealed Word--a function not shared in by the Universal House of Justice. The House of Justice was given the function of legislation--a power not possessed individually by the Guardian. However, when one speaks of the House of Justice as merely a "legislative body," one makes the same limiting error as one who refers to the Guardian as solely an interpreter. The Guardian had broad powers, and so does the House of Justice.
One of the unique powers possessed by the Guardian, was the power to appoint Hands of the Cause of God--unique individuals who carried out important functions in the Baha'i community (Will and Testament of Abdu'l-Baha, p. 12). The Hands of the Cause were under the "direction" of the Guardian of the Cause (Will and Testament, p. 13) Early in the ministry of the Universal House of Justice, the House of Justice determined that it could not appoint more Hands of the Cause; however, it possessed the power to direct the Hands of the Cause, under its general power, i.e. that all of the Baha'is must "turn" to it. In like manner, the Universal House of Justice was designed to guide the national and local houses of justice; but in the absence of the Universal House of Justice, these institutions were guided by the Guardian of the Cause, as the Will and Testament provided that "all" must turn to the Guardian.
Similarly, the Will and Testament specifies that the institution of the Right of God (Huquq'u'llah) was to be offered through the Guardian of the Cause (Will and Testament, p. 15). In a Tablet, Abdu'l-Baha stated that the Right of God was payable to the marja'. This is an Arabic word meaning the center in the Cause to which everyone must turn. This word appears in the Will of Abdu'l-Baha, with reference to both Shoghi Effendi (unto him everyone "must turn" p. 11) and the Universal House of Justice ("unto this Body all things must be referred", p. 14) In one of His Tablets Abdu'l-Baha states that the Universal House of Justice is the marja'. On the strength of this Tablet, the Universal House of Justice determined that it is authorized to receive and disburse the Right of God. This matter is fully discussed here. The point is the flexibility of the Covenant of Abdu'l-Baha, that God endowed both of His Successors--the Universal House of Justice and the Guardian--with broad powers, sufficient for either to lead the Cause independently of the other.