About the Mystery of the Letters the mid-6th century, in which Mar Saba had played an important role. The anonymous author of the treatise declares he was prompted to the study of the secret meanings of the letters by the words of the Apocalypse, "I am the Alpha and Omega", and that he subsequently received a vision about them on Mount Sinai. The author proposes a re-modelled Greek alphabet reduced to 22 letters on the model of the 22 letters of Hebrew (discounting Xi Ξ and Psi Ψ), and with the Hebrew letter names. He then interprets these letters as symbolic figures of 22 works of
Hebrew alphabet with a niqqud symbol – a vowel diacritic (whether or not the diacritic is marked), whereas and ע are considered to be mute, their role being purely indicative of the non-marked vowel. "Niqqud" is the system of dots that help determine vowels and consonants. In Hebrew, all forms of "niqqud" are often omitted in writing, except for children's books, prayer books, poetry, foreign words, and words which would be ambiguous to pronounce. Israeli Hebrew has five vowel phonemes, , but many more written symbols for them: By adding a vertical line (called "Meteg") underneath the letter and to the left