That is the express reason with which Thomas Bulfinch wrote his "Mythologies", because his pupils were having trouble understanding English poems because they couldn't figure out allusions to mythology. Reading that small book could "unlock" a lot of English literature for one.

This is true of much English writing before the 19th Century, and poetry even to a later date. No knowledge of the Bible or mythology and a lot of the writing loses its punch, even if you understand it in the literal sense.