Uncle Dave, it's just the difference between a short "e" sound and a short "a" sound.

I realize that most of the time we "Yanks" tend to pronounce "hairy," "Harry," and "cherry," "marry," all with the same short vowel sound, but strictly speaking there is a difference.   Some Brits, for example, clearly pronounce the name "Carrie" with a short "a" sound, NOT rhyming it with "merry" or "cherry" (short "e"). Say "ca" as in "cat" or "ma" as in "mat" and attach the syllable "ree" to it.   Now say "te" as in "teflon" or "be" as in "bed" and attach the "ree" syllable.
See (hear) the difference?

"Marry" is "ma" (as in "mat") + "ree." "Merry" is "me" (as in "medicine") + "ree."   My dad said "Mary" was supposed to be pronounced "May - ree."

Hardly anyone I know, this side of the pond, anyway, makes those pronunciation distinctions.