That's a really good question, box. I sometimes wonder to myself about the need for an 'afterlife.'
For me, it's all bound up with my experience in this life of a God who loves. My life feels immeasurably fuller with experience of this God, and moments of knowing this in clarity give me an an enticing glimpse into what eternity with God would be like. To be honest, if I didn't believe in God, I don't think I'd be fussed about the idea of an afterlife - the idea of just living again in some kind of unknown realm seems so strange and not particularly attractive, I'd prefer to simply cease being, so I can totally understand why you feel this way.
It's really hard to explain - for me, when I worship God there is a sense of rightness, of everything coming together, of incredible beauty and I know there is more and greater of that to come, and I can't wait. I look at all the goodness and beauty in this world around us, and think about how the bible promises that all will be renewed and restored to what it should be, all suffering will end, and also justice will be done, so all loose ends will be tied. I can't get my head round the idea of 'eternity' really, it seems extraordinary and a completely barmy thing to believe in, doesn't it
- but that's Christian faith for you!
This is a purely Christian perspective, though. My ideas of 'afterlife' (a term I actually don't really like, it has connotations of floaty ghosties and zombies) are more to do with eternity with a God I have come to love than re-uniting with loved ones - though obviously I hope very much to do so.
I'd be interested to hear ideas of why people believe in an afterlife from other perspectives too.