Every alphabetic script in use today descends from a West Semitic invention. Somewhere in the first half of the second millennium BCE, speakers of a West Semitic language, apparently working in an Egyptian setting, took Egyptian signs and used them for the first sound of the Semitic word each sign depicted, producing a small set of consonant letters instead of a syllabary or a logography. The inscriptions from Serabit el-Khadim in Sinai and from Wadi el-Hol in Egypt are the earliest witnesses to it.
That system became the Phoenician alphabet of twenty two letters, and from it came Greek, which added vowels, and so Etruscan and Latin; Aramaic, and from it Hebrew square script, Nabataean and then Arabic, and the Brahmi derived scripts of India and Southeast Asia; and the South Arabian letters that produced Geez. David Sacks's history of the Latin letters traces one line of that descent for general readers.
The religious consequence is not incidental. A writing system with twenty two signs can be learned by someone who is not a professional scribe, and every scriptural religion of this family assumes a readership rather than a priestly monopoly over the text. The technology of the alphabet and the theology of the book arrived together.