(My guess) IMHO, letters are originated from pictographs, as way to script pronunciation of an unknown word (e.g. name of a foreigner) by first sound of word re

(My guess) IMHO, letters are originated from pictographs, as way to script pronunciation of an unknown word (e.g. name of a foreigner) by first sound of word represented by a pictograph. Later, they are adopted to represent foreign speech as is (e.g. to learn it), then letters are adopted by foreigners for their own use. To remember all these symbols and their pronunciation, a mnemonic is necessary: a well known short speech, and list of letters for first sound of each word of this speech. From there, alphabet is derived naturally.