Might be the other way around - rather than emotional cope, being an inducement for greater aggression. If you, the powerful men of your society, can convince all the little folk that dying in battle is way cool and will get them huge rewards in the afterlife, you suddenly become much more powerful, man-for-man, against neighboring polities of similar culture (at least until they adopt that aspect of theology or a similar one)
Might be the other way around - rather than emotional cope, being an inducement for greater aggression. If you, the powerful men of your society, can convince all the little folk that dying in battle is way cool and will get them huge rewards in the afterlife, you suddenly become much more powerful, man-for-man, against neighboring polities of similar culture (at least until they adopt that aspect of theology or a similar one)
It could also be psychological warfare, pretending that your soldiers are ready to die in battle makes enemies less likely to fight back.
And it’s indoctrination as well so that you have more people to join your army.