Both Uses of

immortal
in
Gone with the Wind

Did the honorable Ashley ever jeopardize his immortal soul by kissing you?†
Chpt 3.17 *

Only my masculine pride, my self-respect and, if you choose to so call it, my immortal soul.†
Chpt 4.41

Definitions:

(1) (immortal)
living or existing forever

or:

someone famous throughout history

or:

someone who will never die -- such as a mythological god
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

More rarely, "The Immortals" denotes a military corps of the Persian Empire. The Immortals were so-named because each time a member of the 10,000 man corps was killed or seriously wounded, he was replaced by another man. They are best remembered in western culture for their role in defeating the badly out-numbered Spartans at the Battle of Thermopylae.