A reader writes:
I think of Eternity in terms of one day at a time. Would I rather not die today? Yes, I think I would rather not. Carry that into the future, and you've got Eternity.
There's no point in trying to comprehend what Eternity would be like, because we couldn't comprehend it even if we were living it. The human brain has only so many cells in which to store so many memories. Long before a thousand years pass by, and assuming we had the technology to do so, you'd have to perform a 'spring cleaning' on your brain and decide which memories to keep and which to discard so that you could have room to store new memories.
In effect, thanks to the memory storage limitation of the human brain, we are immune to Eternity. Therein, of course, lies good and evil.
If we had the technology to reverse the aging process, the big deal wouldn't be about the existential crisis of facing Eternity, it would be about the sociological crisis of one generation never making way for the next. Imagine New Kids on the Block plotting a comeback every decade for the next thousand years, and you'll see what I mean.