The Eternal Now
Eternity is one of those mysteries that we can't really wrap our minds around without our heads hurting a bit. It doesn't mean to simply go on without end. It means existing outside time or, put another way, existing in every moment of time. This is God's view of things, which makes a big difference both in our primary creation as Tolkien understood it and in Middle-earth.
From the importance it puts on free will, it's obvious that Catholic belief has no place for predestination. We believe that the paradoxes that predestination tries to resolve are just that: paradoxes. They seem contradictory to us because we live within time, but God sees things from a different angle (to put it mildly). Predestination is incompatible with God's point of view, because God has no "pre." God also has no "post." God exists in the Eternal Now - present in creation not only everywhere but everytime; time is as much a part of God's creation as is place, so God is limited by neither. Albert Einstein wasn't Catholic (so I can't put this quote in a little box on the page), but his statement that "The only reason for time is so that everything doesn't happen at once," fits in here; we'd be overwhelmed if everything happened at once - God isn't.
This is where we get the flip side to all the "what if's" that occur in LotR because of the importance of free will, which we'll look at later. There's a saying that, "With God there are no what if's." For this to be anything but a platitude, we need to think of it in terms of the Eternal Now. We might ask, "What if the Ring had been found by an orc instead of by Bilbo?" And God might reply, "It isn't." Although we humans have to think things out and make decisions one by one, based on previous events and earlier choices, God doesn't need to work that way. Even when we talk about "God's plan," we're talking in terms we understand about something that's beyond our comprehension. Can we really call something that's carried out in the Eternal Now a "plan"? It can be entertaining, and sometimes enlightening, to speculate on some of the "what if's" in LotR, but that's because of our human limitations. God doesn't look at things that way. If we can begin to try to wrap our minds around God's point of view regarding time, many events in LotR make sense in new ways.
Some of these events are our "why's" and "what if's." Before I began understanding things this way, I used to say that in LotR God's plan seems to be existential, because it takes each moment and each free will decision as it occurs and goes from there. For example, Faramir is sent a message in a dream that indicates he should go to Rivendell, but Boromir goes instead. Is this the end of the divine plan for the two brothers? Does Providence say, "Well, you messed that up, so just forget it. Gondor is doomed"? No, Providence by whatever name takes that situation as a given. At his death, Boromir has achieved a wisdom he might never have reached if he had stayed home. When Frodo and Sam are captured in Ithilien, they're taken by Faramir, the brother who's less likely to shoot first and ask questions later. But, looked at another way, this isn't existential at all. God doesn't "change plans" when things such as this happen, because to God none of it is unexpected. It occurs within the Eternal Now. In the story's most central example, Frodo is given the grace necessary for the part he plays in the destruction of the Ring: no more and no less. What if Gollum hadn't been at the Sammath Naur? Tolkien joins in the speculations on that question, but not even he knows the answer because Gollum was there. God doesn't need contingency plans or answers to "What if?" (Although at times God does seem to understand our need to ask the question.)
Other events which the Eternal Now helps explain involve foretellings: the verse that eventually brought Boromir to Rivendell, for example, and the prophecy that "no man" would kill the Witch-king. What if, say, Éomer had killed Sauron's Number One? Again, speaking from outside time, God would say, "He doesn't." God doesn't make predictions; God sees what is - in every place and at every time. Of course, in order to tell us finite, time-challenged people about it, God needs someone faithful to receive the message and to speak it. At the very end of The Hobbit, there's an interesting exchange about prophecies. In response to Balin's description of how the 'rivers run with gold' at the Lonely Mountain, Bilbo says, 'Then the prophecies of the old songs have turned out to be true after a fashion!' Gandalf responds:
'Of course!' said Gandalf. 'And why should they not prove true? Surely you don't disbelieve the prophecies, because you had a hand in bringing them about yourself? You don't really suppose, do you, that all your adventures and escapes were managed by mere luck, just for your sole benefit? You are a very fine person, Mr Baggins, and I am very fond of you; but you are only quite a little fellow in a wide world after all!'
When Tolkien wrote those words, not even he realized how true they were, since Bilbo's 'adventures and escapes' included the very important finding of the Ring. Not mere luck - an act of Providence.
But I believe the most important way the Eternal Now affects The Lord of the Rings is in the way that the presence of "the One never named" is "felt on every page," and in the way that those on the side of Good respond to that presence without being able to name it. Middle-earth is pre-Christian, but that doesn't mean its people are unaffected by Christ's presence in creation that unites it to God, because that presence exists in the Eternal Now. They simply don't know about it yet.