Bahá’u’lláh’s preeminent doctrinal work as well as His second longest, answering four questions from an uncle of the Báb regarding prophetic expectation and fulfilment, affirming the essential unity of the prophets of God while simultaneously acknowledging the distinctiveness of their persons and missions, expounding the concept of progressive revelations from God that are renewed about every thousand years, summarizing the spiritual prerequisites of the seekers on the spiritual path, clarifying the central role in that path of the independent investigation of reality, condemning the clergy for their role in the rejection of the prophets from age to age, and emphasizing, through a commentary on certain verses of the gospels, the need for a symbolic as opposed to a literal understanding of sacred scriptures.