The cult of the dead is rationally based on the belief in the supra-temporality of the soul, but its irrational basis is to be found in the psychological need of the living to do something for the departed.
This is an elementary need which forces itself upon even the most “enlightened” individuals when faced by the death of relatives and friends.
That is why, enlightenment or no enlightenment, we still have all manner of ceremonies for the dead.
If Lenin had to submit to being embalmed and put on show in a sumptuous mausoleum like an Egyptian pharaoh, we may be quite sure it was not because his followers believed in the resurrection of the body.
Apart, however, from the Masses said for the soul in the Catholic Church, the provisions we make for the dead are rudimentary and on the lowest level, not because we cannot convince ourselves of the soul’s immortality, but because we have rationalized the abovementioned psychological need out of existence.
We behave as if we did not have this need, and because we cannot believe in a life after death we prefer to do nothing about it.
Simpler-minded people follow their own feelings, and, as in Italy, build themselves funeral monuments of gruesome beauty.
The Catholic Masses for the soul are on a level considerably above this, because they are expressly intended for the psychic welfare of the deceased and are not a mere gratification of lachrymose sentiments. ~Carl Jung, CW 11, Para 855