Afterlife myths invoke the transporter paradox and the ship of Theseus.
The transporter paradox questions whether Captain Kirk on the ship is the same person as Captain Kirk once he beams down to a planet. Sure, he has the same molecular structure, the same brain in the same state as when he departed, but there is energy loss, and we know that at a small enough scale planet Kirk is not rebuilt exactly as ship Kirk was taken apart. Is it the same guy, or two different identical guys? (It gets worse when Picard dies and is reassembled from transporter memories and nobody talks about that incident ever. )
The thing is, we exist in life as an active brain running neuron processes continuously (mostly -- I get to that). When we die, these processes stop. Our brain matter dies out. Our neurons fire for the last time. The engine that allows us to sense, perceive, process, think and respond ceases to function. It's not merely a matter of one's soul being transported to eternal fire. My soul could go to the heart of the sun (15,000,000℃!) and without active nerve endings, not feel a thing or know where it is.
In order to experience the glory of Heaven or the torments of Hell or the delights of paradise, a new mechanism would have to manifest that mirrored the material brain, but in this case, the new device is distinct from the old one. If it counts, then so would DeepSouth (the computer) loaded up with brain emulation software, and the scanned memories of Jeff Bezos or Elon Musk. (You know they're working on this right now.) And billionaires and princes will soon exist after death as emulated brains in giant mainframes... while a spiritual poppet of them allegedly experiences dozens of afterlives, according to various religions.
IRL, our existence continues entirely based on the assumption of continuity. In delta sleep (which we do nightly for fifteen minutes to two hours) our cognitive brain goes dormant while our bodies repair and grow new bits. REM sleep might be the process of rebooting and reacquiring who we are and what's on our to-do list. And then there's the matter that with new experiences and new data, who we are changes continuously, if slowly. The ship of Theseus is swapped out, cleat by cleat and pin by pin, and who we are changes with that.
The grim reality of death is seen most clearly with the onset of dementia and diseases in which mental faculties deteriorate, and we watch as who that person is fades away one memory, one capacity at a time. In these tragedies, more than any other, we see that who we are is in the living process, and when it ceases, ultimately, so do we, and all your money (or piety) won't another minute buy.