Twice the size of the Kitáb-i-Íqán, it contains insights into the prophecies of the Báb concerning 'Him Whom God shall make manifest' and was written in defence of the Baháʼí Revelation.
Shoghi Effendi referred to the work as Baháʼu'lláh's "apologia, written to refute the accusations levelled against Him by Mírzá Mihdíy-i-Rashtí, corresponding to the Kitáb-i-Iqan, revealed in defense of the Bábí Revelation".
[2] The book consists of short quotes from Mírzá Mihdí's letter followed by numerous pages refuting each argument.
A major portion of the work is devoted to explaining the Báb's prophecies concerning 'Him Whom God shall make manifest'.
He includes numerous quotations from the Báb's writings, such as the following (referring to 'Him Whom God shall make manifest'): Baháʼu'lláh includes strong language concerning Mírzá Mihdíy-i-Rashtí, whom he refers to as the 'wicked one', 'the evil plotter', 'the impious', 'the impudent', 'the outcast', 'the faithless soul', 'the froward', and 'he who contends with God'.