This book was written partly in Persian and partly in Arabic by Baha'u'llah the prophet founder of the Baha'i Faith in 1862. At this time Baha'u'llah was living as an exile in Baghdad, then a part of the Ottoman Empire. This book is an answer to the questions posed by a maternal uncle of the Bab concerning the validity of the cause of the Bab, and then it was written within two days and nights. It constitutes the major theological work of Baha'u'llah, and hence of the Baha'i Faith. It is sometimes referred to as the completion of the Persian Bayan.

The book is in two parts: the first part deals with the foundational discourse that divine revelation is progressive and religions are related to one another, with each major monotheistic religion accepting the previous ones and often in veiled terms, preaching the advent of the next one. Since the questioner is a Muslim, Baha'u'llah uses verses from the Bible to show how a Christian could interpret his own sacred texts in allegorical terms to come to believe in the next dispensation.

The second and larger part of the book is the substantive discourse and deals with specific proofs, both theological and logical, of the mission of the Bab.