The Book of Certitude
One of the foremost books of the Revelation of Bahá'u'lláh, the Kitáb-i-Iqan contains Bahá'u'lláh's explanations of the basic tenets of the Bahá'í Faith and of the continuity of religion as it has been revealed throughout the ages. This book affirms the unity of the Prophets, the universality of Their Message, the identity of Their fundamental teachings, the sanctity of Their scriptures, and the twofold character of Their stations.
The book elucidates allegorical passages from The New Testament and the Qur'an that have caused misunderstandings among religious leaders. Termed by Shoghi Effendi "the most important book written on the spiritual significance of the Cause," it should be "read and read over again by every soul who desires to serve" Bahá'u'lláh.