“Knowledge is twenty and seven letters. All that the Prophets have revealed are two letters thereof. No man thus far hath known more than these two letters. But when the Qá’im shall arise, He will cause the remaining twenty and five letters to be made manifest.”

 

"Wishing to stress the sublimity of the Báb’s exalted station as compared with that of the Prophets of the past, Bahá’u’lláh in that same epistle asserts: “No understanding can grasp the nature of His Revelation, nor can any knowledge comprehend the full measure of His Faith.” He then quotes, in confirmation of His argument, these prophetic words: “Knowledge is twenty and seven letters. All that the Prophets have revealed are two letters thereof. No man thus far hath known more than these two letters. But when the Qá’im shall arise, He will cause the remaining twenty and five letters to be made manifest.” “Behold,” He adds, “how great and lofty is His station! His rank excelleth that of all the Prophets and His Revelation transcendeth the comprehension and understanding of all their chosen ones.” “Of His Revelation,” He further adds, “the Prophets of God, His saints and chosen ones, have either not been informed, or, in pursuance of God’s inscrutable decree, they have not disclosed.”

 
Bahá’u’lláh cited by Shoghi Effendi

(The World Order of Bahá’u’lláh)
www.bahai.org/r/659633392