c. 1200, gloire "the splendor of God or Christ; praise offered to God, worship," from Old French glorie "glory (of God); worldly honor, renown; splendor, magnificence, pomp" (11c., Modern French gloire), from Latin gloria "fame, renown, great praise or honor," a word of uncertain origin.
The etymology as *gnoria "knowledge, fame" to gnarus "known" and i-gnorare has been acknowledged by some scholars, and rejected by others. In its favour speak the semantics of words for "glory", which in Indo-European societies mostly have to do with "spoken praise", "reputation by hearsay". Against the assumed etymology speak the phonetics. [de Vaan]
Meaning "one who is a source of glory" is from mid-14c. Also in Middle English "thirst for glory, vainglory, pride, boasting, vanity" (late 14c.), Sense of "magnificence" is late 14c. in English. Meaning "worldly honor, fame, renown." Latin also had gloriola "a little fame." Glory days was in use by 1970. Old Glory for "the American flag" is first attested 1862.
The Christian sense are from the Latin word's use in the Bible to translate Greek doxa "expectation" (Homer), later "an opinion, judgment," and later still "opinion others have of one (good or bad), fame; glory," which was used in Biblical writing to translate a Hebrew word which had a sense of "brightness, splendor, magnificence, majesty of outward appearance." The religious use has colored that word's meaning in most European tongues. Wuldor was an Old English word used in this sense.