"letters of a language arranged in customary order," 1570s, from Late Latin alphabetum (Tertullian), from Greek alphabetos, from alpha + beta. Attested from early 15c. in a sense "learning or lore acquired through reading." Words for it in Old English included stæfræw, literally "row of letters," stæfrof "array of letters," and compare ABC.
It was a wise though a lazy cleric whom Luther mentions in his "Table Talk,"--the monk who, instead of reciting his breviary, used to run over the alphabet and then say, "O my God, take this alphabet, and put it together how you will." [William S. Walsh, "Handy-Book of Literary Curiosities," 1892]
Alphabet soup first attested 1907.