Eternity is not just more time, in a sense similar to how God is not just a bigger cause. As God is the Cause of causes – the Unmoved Mover, in classic Greek philosophy, wherein, in Christian theology, all created things live and move and have their being – eternity is that within which time takes place. Eternity is more than the sum of all time.
This has implications for redemption and repentance. We, bounded by time, find it strictly unimaginable (strictly, since our acts of imaginations are realized over time) that a creature could act eternally. Angels are such creatures. We, having been given eternal life, are also such creatures, though we haven’t (in both senses of that word) realized it yet.
When we talk of the fall of Satan and a battle in Heaven, we are speaking about events that take place (if that’s a meaningful way to say it) in eternity – they are not something that happened in the past. Satan is falling now, has fallen in the past, will continue to fall in the future – that’s how events in eternity necessarily look to us living in time, like seeing a 2-dimensional slice of a three dimensional figure, and trying to imagine the figure – only it’s worse, since eternity is not just the sum of a bunch of snapshots of time.
People sometimes wonder if Satan or any human in Hell can repent and be saved. If eternity were just more time, then that would be an interesting question. But if eternal acts are eternal, there is no ‘later’ in which to reconsider or be redeemed. This will be our fate once we realize, in the sense of make real to our own eyes, our eternal nature. This is why saints, as they start to see God, are mortified by their slightest fault – becoming more Christ-like is also becoming more aware of their own eternal nature, and how their sins tend to become eternal as a result.
So here’s the mind-bender: Satan and his angels knew all this. Their ‘act’ in falling away from God included all the temptations, manipulations, possessions and horrors by which we see evil unveiled over time – and their defeat at the hands of Christ. All these acts took place at once, as it were, as it was, is now and ever shall be. The fall of the angels IS the evil they work in the world and our lives. There was no ‘before’ Satan fell, and no ‘after’. He is falling now; he is rejecting God now; he is hating us with a white-hot passion now. And he will be doing all this for ever – for all eternity.
The fallen angels knew all this, saw how it worked out to their own destruction and pain, and rejected God anyway.
Christianity proposes we all get to make eternal decisions, that there comes a point where we pass from time within which one can change one’s mind, to eternity, where knowledge and decisions are complete.