"What "oppression" is greater than that which hath been recounted? What "oppression" is more grievous than that a soul seeking the truth, and wishing to attain unto the knowledge of God, should know not where to go for it and from whom to seek it? For opinions have sorely differed, and the ways unto the attainment of God have multiplied. This "oppression" is the essential feature of every Revelation. Unless it cometh to pass, the Sun of Truth will not be made manifest. For the break of the morn of divine guidance must needs follow the darkness of the night of error. For this reason, in all chronicles and traditions reference hath been made unto these things, namely that iniquity shall cover the surface of the earth and darkness shall envelop mankind. As the traditions referred to are well known, and as the purpose of this servant is to be brief, He will refrain from quoting the text of these traditions.
Were this "oppression" (which literally meaneth pressure) to be interpreted that the earth is to become contracted, or were men's idle fancy to conceive similar calamities to befall mankind, it is clear and manifest that no such happenings can ever come to pass. They will assuredly protest that this pre-requisite of divine revelation hath not been made manifest. Such hath been and still is their contention. Whereas, by "oppression" is meant the want of capacity to acquire spiritual knowledge and apprehend the Word of God. By it is meant that when the Day-star of Truth hath set, and the mirrors that reflect His light have departed, mankind will become afflicted with "oppression" and hardship, knowing not whither to turn for guidance. Thus We instruct thee in the interpretation of the traditions, and reveal unto thee the mysteries of divine wisdom, that haply thou mayest comprehend the meaning thereof, and be of them that have quaffed the cup of divine knowledge and understanding.
(Baha'u'llah, The Kitab-i-Iqan, p. 31)