Tolkien wrote Leaf By Niggle in 1939. If you have not read it before, take the time now. It is a short piece. Of Niggle's intended masterwork painting of a tree and forest only a single leaf remains after he is called away on an unexpected journey and those in charge of his estate treat his work carelessly. It is easy to make an automatic equivalence between this leaf and Tolkien's incomplete epic. Though the vast outline of Middle-Earth that would eventually become The Silmarillion was much in place, the episode from the Third Age that he wished to develop was barely started. The Hobbit had been published and an audience was already clamoring for more, but it would be two years before Frodo and Sam would meet Aragorn at the Prancing Pony, and even then, Tolkien did not have a clear idea who Aragorn was. He despaired of any of it ever being finished. In fact the "New Hobbit" was not finished for another 15 years, and The Silmarillion not completed until more than 20 years after that.
It is worth noting as an aside that it would not have been finished had it not been for Lewis.
Both works were enormous in both scope and length. There is an artistic technique of making something appear large at first, but then reveal it to be quite small when contrasted with a still-larger object and then a third object more massive still as in "Star Wars: A New Hope" from the initial space fighter through the Death Star. One gets some sense of that when reading the Tolkien legendarium in the usual order, beginning with The Hobbit. It seems a large-enough world, larger by far than the usual setting of a children's book in a town or animal burrow. The greatness and distance of journeys to unknown places is part of the story, of a halfling unexpectedly out in the wide world. Yet one is only a few pages into The Fellowship of the Ring before perceiving that the horizons are spread much farther, the adventure much deeper and deadlier. Throughout The Lord of the Rings the adventure keeps growing, with references to events farther away and deeper in the past, until these are outlined along a history of thousands of years in the appendices.
This is dwarfed in turn by the Ainulindalë, a creation-story that opens The Silmarillion, describing a time before time. Bilbo journeying all the way to Dale no longer seems such a great distance. It is only "there and back again."
Tolkien stated he disliked allegory and chided Lewis for an Aslan who is too obviously Christlike (though as I recently noted, he disliked the first Narnian chronicle before the Lion had even made an appearance. We must not assume that authors know their own minds so well as they think.) Yet there isn't much other way to read "Leaf, by Niggle." He tried to deny it and described it as at most an evocation and symbol of the creative and subcreative process, but that wouldn't be much of a difference to begin with, and in execution, I don't see a distinction here. He may have intended to only suggest this world, Purgatory, and Heaven, but it fairly leaps out at the reader. As he wrote it he may also have not been thinking only of Middle-Earth but of a dozen other creative and academic projects, but again, he does not fully know his own mind. The later reader knows his biography and his obsession with the vast tale and his attention to getting details just so. The "leaf" is some part of a tree and forest that he worked on and hoped some piece would survive. Yet by the end, when that incomplete work has been fashioned into a fuller world by God, becomes inhabited, and gets a name and a permanent use in the grand scheme of heaven, it is still just a little corner, noticed by only a few.
That ending comes closest to Tolkien's thought about his own work. However vast the events of the end of the Third Age, and even Ea itself seem when one is inside, whether to write them or read them, he knew they were only a prefiguring of the events of the incarnation and resurrection, a border skirmish in the lead up to the Great War of Heaven. In later years he noted this in his correspondence a few times, according to Milton scholar Janet Knedlik. (I don't have the references myself.)
So are all the works of man. Our great events are but border skirmishes. However, they are our border skirmishes, to which we have been assigned, and granted the grace that our actions do mean something even in the Great War.