In Charles Williams' novel Descent into Hell the climactic scene is when Pauline Anstruther offers herself (in what Williams refers to as 'exchange') to suffer - by 'substitution' of herself - the fear and pain of an ancestor who is being burned at the stake for (Protestant) heresy.
I always regarded this idea of prayer working backwards in time as at best incomprehensible and at worst insane (and leading to intractable confusions).
But yesterday I (at last) 'got it' - as an example of the difference between living in (human) time and living in (divine) eternity - out of time; that is, an example of argument of Boethius in Consolation of Philosophy.
It is illustrative that it has taken me considerably more than a year to make this link-up, more than a year since studying and thinking about this classic book.
So, it is clear that although I thought I understood the point made by Boethius (and explained elsewhere - e.g. by CS Lewis in Mere Christianity) - I didn't really understand it.
It is very important, because understanding this point clarifies why it is reasonable (i.e. in accordance with reason) to pray for the dead, to pray concerning things that have already happened - indeed to pray about anything and everything. What seems backwards in time or in reverse of causality to us; is not so for God.
(Of course (fortunately!) it is not necessary to understand these things in order to do them; nonetheless lack of understanding can be a stumbling block.)
I think I do understand it now - but I would still find it very difficult to explain both briefly and comprehensibly
From C.S Lewis: Mere Christianity:
Everyone who believes in God at all believes that He knows what you and I are going to do tomorrow. But if He knows I am going to do so-and-so, how can I be free to do otherwise?
Well, here once again, the difficulty comes from thinking that God is progressing along the Time-line like us: the only difference being that He can see ahead and we cannot.
Well, if that were true, if God foresaw our acts, it would be very hard to understand how we could be free not to do them.
But suppose God is outside and above the Time-line. In that case, what we call "tomorrow" is visible to Him in just the same way as what we call "today." All the days are "Now" for Him. He does not remember you doing things yesterday; He simply sees you doing them, because, though you have lost yesterday. He has not.
He does not "foresee" you doing things tomorrow; He simply sees you doing them: because, though tomorrow is not yet there for you, it is for Him.
You never supposed that your actions at this moment were any less free because God knows what you are doing. Well, He knows your tomorrow's actions in just the same way-because He is already in tomorrow and can simply watch you.
In a sense, He does not know your action till you have done it: but then the moment at which you have done it is already "Now" for Him."