Our brain has a desire to continue, an innate drive for survival. The survival instinct seems fundamental to all living things. Natural selection is the natural enemy, the impartial selection of evolved survival skills fundamental to individual continuance and the opportunity for procreation.
Essentially it is an acquired response instinct (fight or flight), an algorithm to utilize the mathematical processes in nature. IMO, this is why the brain has invented the concept of an abstract afterlife and the requirements of becoming qualified in attaining that status.
The meaning of human existence is the drive for continuance of existence. It isn’t complicated.