early 14c., "the sacred writings of the Bible, the books of the Old and New Testaments" (in this sense commonly with a capital); from Medieval Latin and Late Latin scriptura "the writings contained in the Bible, a passage from the Bible," in classical Latin "a writing, character, inscription," from scriptus, past participle of scribere "to write" (from PIE root *skribh- "to cut").
The word in Middle English also could mean "a writing, an act of writing, written characters" (mid-14c.), a sense now rare. The sense of "a passage from the Bible" is by late 14c. Figuratively, of something assuredly true, it is attested by 1570s. As an adjective, "relating to the Scriptures," by 1720.
Scripturalist for "one who adheres literally to the Scriptures and makes them the foundation of all philosophy" is perhaps by 1725, certainly by 1857; earlier in this sense was scripturarian (1670s), scripturist (1620s). Related: Scripturalism.