This is, of course, the most quintessentially unanswerable question. But I shall have a go, nevertheless.
First, let's take the most literal interpretation of life after death. Namely, that your personal identity, complete with the memories of your life, your intellectual faculties and possibly also some kind of body image (even if not fully material) is preserved in some kind of heaven. Let's think about what that heaven would be like. Is it full of the souls of every human who has ever lived? How far back do we go? Did cavemen go to heaven? Did australopithecus? At what point in history were our ancestors granted souls? Was heaven just empty before that, waiting for us to evolve to the level of sophistication to gain entrance? Or do all living things have souls? If only humans have souls, does that mean that we have no animals for company in heaven? So we can’t play with our pets, ride a horse, go fishing. Interaction with our natural environment is quite a big part of human existence so heaven without animals would be quite a bland place. On the other hand, if all living things go to heaven it would be a pretty busy place. Animals with short lifespans would vastly outnumber those with longer ones. For every wolf, there would be a thousand rabbits and a billion flies and slathered on top of all of that would be a thick fetid layer of bacteria, choking everything else.
Maybe we are provided with pretend, spiritual, versions of animals as part of the set dressing of heaven. But even if you just consider the human population of heaven, there are problems. Part of our essential sense of identity is the ability to form new memories and learn things. In life we have just 70 or 80 years to do this but the people that died in the Old Testament have been in heaven for 6,000 years. How would their mental processes have changed in that time? Would we get to heaven and find that we are intellectual gnats next to the incredible wisdom that they would have accumulated? Would they find they had nothing to say to us? Conversely, if everyone who dies is held in some kind of state of suspension, waiting for Judgement Day and we all go to heaven at the same time, wouldn’t we feel vastly superior to the guys from 4000BC? Either way, this would surely result in feelings of resentment and segregated cliques would develop along cultural and historical lines with tension, argument and maybe even violence between groups.
But maybe the afterlife isn’t such a literal transposition of our earthly existence at all. Maybe our spirits are all fused together to form part of some universal consciousness - we become one with God, in other words. That’s easier to imagine in some ways, but can we really call it an afterlife? If your memories and thoughts and understandings are all connected to and merged with the memories, thoughts and understandings of every other person that has ever lived, are you still “you”? It’s hard to see how any meaningful definition of the self could persist through such a process. Even if you were, somehow, able to retain the awareness of your past mortal life and all its memories, those 80 years of one person’s life would be completely dwarfed by your new awareness of 10,000 years and 20 billion lives. How could any of the things that had happened to you when you were alive still seem important enough in that boiling mixture for you to use them as the basis for defining who you were? You used to be an unfertilised egg and a sperm but you don’t think that any of the “experiences” of those individual gametes is part of who you are now. They created you but they were not you. What you are is the sum of your experiences and memories since birth. In the same way, a fused consciousness consisting of the souls of everyone that dies would surely not regard the mortal portion of existence as being part of what defines identity.
The third main possibility is that heaven is a construct maintained by God as some kind of reward for our mortal toil. Being an omnipotent entity, God could presumably create a kind of simulator for each of us where we exist in a perfect version of our previous life, complete with perfect representations of people we have known and loved. For it to be perfect, the other people would have to have their behaviours and reactions tailored specifically to ours so they couldn’t be the real versions. If your wife is secretly having an affair when you are both killed in a car crash, she will want her lover in her heaven; but in your heaven, not only will he not be there, your wife won’t want anyone but you. God can arrange this because he can do anything, and he also makes sure that these angelic forms never get boring to talk to, or bored by us. It’s all just fluffy clouds and kittens and loving family and an adoring, beautiful partner. In other words, heaven is a wonderful dream that lasts forever. But for some of us, at least, simply controlling all the actors and the scenery in this dream wouldn’t be enough to maintain the illusion. God would also need to control us. Because after a few years or decades or millennia, we might start to question how it is that our dream wife never argues with us or complains about us or gets bored with us. And equally, we might get bored with the same limited set of people around us. And while God could fix some of these things by adjusting the simulation around us, eventually we would grow dissatisfied with whatever variation he supplied. This is part of human nature. And to fix this, God would have to adjust our own desires and ambitions and interests. Being omnipotent of course, he could easily preserve us in a perfect state of rapture for the rest of eternity. But is this actually an after*life*? Or is it simply an endlessly stretched freeze-frame moment of pure joy? In other words, we are back to the question of whether you would still be *you* in those circumstances. As with the universal conscious scenario, after fifty trillion years of uninterrupted heavenly grace, it’s hard to see how anything that happened during your brief stay on Earth would have any relevance to who you are now. And since everyone else has been having fifty trillion years of their own heavenly grace at the same time, wouldn’t we all just asymptotically approach the same state? We would all just become motes of light - every individual memory or character or personality trait would eventually be lost to the golden, rapturous, unifying quality of heaven, no matter how carefully tailored to our individual needs it originally was.
So it seems that all of the characteristics that we think of as part of being alive, are intrinsically connected to the temporariness of that life. Being alive is all we have ever experienced so it is very hard to imagine a time when we will not be alive. But when you try to create a new, different sort of life that starts when this one ends, what you end up with is something that isn’t actually living at all. Your personal sense of identity is something that only exists because your life is finite. It doesn’t make sense to talk of it surviving indefinitely into the future, anymore that it does to talk of it having existed indefinitely into the past. And as soon as you accept that your sense of self will not persist beyond death, all the other aspects of the various interpretations of the afterlife start to sound like different ways of describing the same thing. When we die, our atoms are recycled and incorporated into new creatures, new landscapes, new stars. Our individual memories are lost but we remain part of the complex swirling entity that is the universe. And if the universe is self-aware, it isn’t an awareness that we can share because we are just tiny specs of dust that clumped briefly together in one pattern before drifting apart to form new patterns somewhere else.