Mortality is, by definition, finite, thus making mortals inherently unqualified to comprehend the scope of eternity. And yet, there is in each of us, a part which once, perhaps, understood. I expect it is that part which makes me spend so much time trying to comprehend this subject I am so unable to understand (remember?). "What's so hard to understand?" you're wondering. It's not the technical definition I ponder. Endless is technically easy enough to understand. It's the implications behind the definitions that leave me pondering.
Mortality, being finite, is full of beginnings and endings. We're surrounded by them, literally. The day begins and ends, as do all other measures of time. We are born. We start school. We graduate. We go to college. We start a new job. We get married. We have children. We get a new car. The car dies and we get another. As much as we may not wish to face it, eventually, we die. On and on the list goes of things that start and end. But when it comes to excitement and other positive feelings, I suspect the balance usually tips in favor of the beginnings, while the endings are more often viewed negatively (or not viewed at all, for the unpleasant helplessness we sometimes feel at their inevitability). The excitement and hopefulness of beginnings and the inevitability of ends may be why we have an easier time, I think, understanding eternity future and a more difficult grasp on eternity past.
Most of us learn the symbol and concept of infinity at a fairly young age in math class: x to infinity, positive infinity, negative infinity. All these have a beginning (or an ending, depending on how you want to look at it). They are infinite in one "direction" only. It's not so hard for us to grasp the idea. By the time we take that math class, we've probably already learned (in a science class) that matter doesn't appear from nothing, nor disappear into nothing. Instead, it changes form. Thus, it's not so hard to understand that something could be infinite, or could exist into the future for the remainder of eternity (if I can put it that way).
Logic then dictates that matter also has no beginning, that it has always existed, in some form. Thus, the piece of firewood that we just so casually converted into ash, smoke and heat for the sake of a few burnt marshmallows, was once something else: a tree, water, nutrients, atoms floating around somewhere waiting to be enlisted in the construction of s'mores. That's easy to think about in terms of math and matter, but not so easy to consider when thinking about that immortal piece of ourselves.
Some believe we are nothing more than matter. To them, I suppose the topic of eternity is no more interesting than a math or science class. But for those of us who believe that part of our current selves (our spirits, if you will) are immortal, it's quite a thing to ponder. As I understand it, some believe that our spirits come into existence at the same time as our bodies. Those who believe that need only consider what they'll be doing for future eternity. But for those of us who believe we have always existed (in one form or another), that past eternity is quite a notion. After all, what could I possibly have been doing for all that time? Is this (looking at self, inside and out) all I've managed to accomplish with an infinite amount of time on my hands? This mortal me wonders, if it took me an infinite amount of time to get here, maybe I don't want to remember eternity past (it might be kind of like childhood, filled with stupid mistakes I'd rather not recall). Still, I'm tempted to wonder, uselessly, just how many years are in an infinity? How long did I spend wandering around the infinite reaches of space like a rich kid with a Eurail pass that never expires? Is it possible to be an immortal couch potato?
And for all of us who believe in that future eternity, how on earth will we keep from getting bored out of our skulls? Oh sure, we're awfully ignorant now, with lots of new things to learn and do, but how many eons will it be before we can respond to every idea, "been there, done that"? I mean, if God knows everything, "everything" must be finite, right? So even if it takes seemingly forever to learn it all, eventually we'll run out of things to learn, and then what?
Perhaps I'll post more on the following later, but not too long ago, I read a newsgroup post by someone wondering about the omniscience and foreknowledge of God and what that implied for the poster's own agency (or "free will"). That got me thinking about omniscience - which seems like it must be closely related to eternity. And in the end, I was left thinking that perhaps "everything" is no more finite than eternity and that omniscience isn't an accomplishment, but a state of being, continually increasing, just as eternity is continually increasing, at least in one direction...
Which brings us right to the heart of my inability to comprehend eternity, specifically, eternity past. If eternity future is continually increasing, and there was no beginning to eternity past, doesn't that imply it's increasing backwards too, extending further and further into the past? I mean, if there was a starting point, then we could just go from zero to infinity, call it eternity and it would be somewhat comprehensible. But there couldn't be a starting point (or everything would have had to have come from nothing, which is ridiculous, so we can rule that out right now). And yet, it's hard to imagine the past increasing - if new stuff is getting added to the past, it is, by definition (being new), not past, but future (or present). And if new stuff isn't getting added to the past, how can it be endless? You see, I'm going in 1 now.
The idea of an infinite past, an eternity extending back from this moment, with no ending, and yet still being already past, is simply beyond my mortal comprehension. And I seem unable to let it be, perhaps because some part of me understands, sort of, but can't put it in words. As soon as I've figured it out, I'll let you know. (Don't hold your breath, please; you'll turn blue.)