What is the Covenant?

What is the Covenant? There have been volumes of books and compilations published on the topic, but this quote from the House of Justice sums it up beautifully:

A Covenant in the religious sense is a binding agreement between God and man, whereby God requires of man certain behaviour in return for which He guarantees certain blessings, or whereby He gives man certain bounties in return for which He takes from those who accept them an undertaking to behave in a certain way. There is, for example, the Greater Covenant which every Manifestation of God makes with His followers, promising that in the fulness of time a new Manifestation will be sent, and taking from them the undertaking to accept Him when this occurs. There is also the Lesser Covenant that a Manifestation of God makes with His followers that they will accept His appointed successor after Him. If they do so, the Faith can remain united and pure. If not, the Faith becomes divided and its force spent. It is a Covenant of this kind that Baha’u’llah made with His followers regarding ‘‘Abdu’l-Bahá and that ‘Abdu’l-Bahá perpetuated through the Administrative Order…

From a letter written by The Universal House of Justice to an individual believer, 23 March 1975