I would also add to this that if there does exist an eternal existence after one's death [1], then it is infinitely rational to spend this comparatively short l

I would also add to this that if there does exist an eternal existence after one's death [1], then it is infinitely rational to spend this comparatively short life finding out what the nature of that eternity is and how best to prepare for it. [1] Which incidentally, I don't think is possible to conclusively prove nor disprove. Like most things in life, you look at the evidence and make your decision.