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 was an abjad consisting only of consonants, but is now considered an "impure abjad". As with other abjads, such as the Arabic alphabet, during its centuries-long use scribes devised means of indicating vowel sounds by separate vowel points, known in Hebrew as "niqqud." In both biblical and rabbinic Hebrew, the letters can also function as "matres lectionis", which is when certain consonants are used to indicate vowels. There is a trend in Modern Hebrew towards the use of "matres lectionis" to indicate vowels that have traditionally gone unwritten, a practice known as "full spelling". The Yiddish alphabet, a modified version