What is the “Lesser Covenant”?

“To direct and canalize these forces let loose by this Heaven-sent process, and to insure their harmonious and continuous operation after His ascension, an instrument divinely ordained, invested with indisputable authority, organically linked with the Author of the Revelation Himself, was clearly indispensable. That instrument Bahá’u’lláh had expressly provided through the institution of the Covenant, an institution which he had firmly established prior to His ascension. This same Covenant He had anticipated in His Kitáb-i-Aqdas, had alluded to it as He bade His last farewell to the members of His family, who had been summoned to His bed-side, in the days immediately preceding His ascension, and had incorporated it in a special document which He designated as ‘the Book of My Covenant,’ and which He entrusted, during His last illness, to His eldest son ‘Abdu’l-Bahá.

Written entirely in His own hand … this unique and epoch- making Document, designated by Bahá’u’lláh as His ‘Most Great Tablet,’ and alluded to by Him as the ‘Crimson Book’ in His ‘Epistle to the Son of the Wolf,’ can find no parallel in the Scriptures of any previous Dispensation, not excluding that of the Báb Himself. For nowhere in the books pertaining to any of the world’s religious systems, not even among the writings of the Author of the Bábí Revelation, do we find any single document establishing a Covenant endowed with an authority comparable to the Covenant which Bahá’u’lláh had Himself instituted.”

Shoghi Effendi, God Passes By, pp. 237-38.

“Bahá’u’lláh, the Revealer of God’s Word in this Day, the Source of Authority, the Fountainhead of Justice, the Creator of a new World Order, the Establisher of the Most Great Peace, the Inspirer and Founder of a world civilization, the Judge, the Lawgiver, the Unifier and Redeemer of all mankind, has proclaimed the advent of God’s Kingdom on earth, has formulated its laws and ordinances, enunciated its principles, and ordained its institutions. To direct and canalize the forces released by His Revelation He instituted His Covenant, whose power has preserved the integrity of His Faith, maintained its unity and stimulated its world-wide expansion throughout the successive ministries of ‘Abdu’l-Bahá and Shoghi Effendi. It continues to fulfil its life-giving purpose through the agency of the Universal House of Justice whose fundamental object, as one of the twin successors of Bahá’u’lláh and ‘Abdu’l-Bahá, is to ensure the continuity of that divinely-appointed authority which flows from the Source of the Faith, to safeguard the unity of its followers, and to maintain the integrity and flexibility of its teachings.”

The Universal House of Justice, The Constitution of the Universal House of Justice.