As an amateur Tolkienist (or whatever term one cares to use), I always find it interesting when articles pop up declaring they've found the key symbols that tie Tolkien's works to his Catholic faith.
In the book Morgoth's Ring, there is a fictitious debate called by Tolkien, 'Athrabeth Finrod ah Andreth'. It is a debate between the immortal Elf Finrod and the mortal woman Andreth. Tolkien uses the debate as an exposition of the relationship of his mythology to the Christian tradition. Included is the description of the Fall of Man and its consequences and the Elvish thought on the end of the world.
After the debate concludes, Tolkien sets out in a 'third person' commentary the motivations of the Elf and the woman and how they look at various topics relating to life, death, evil in the world and the end of the world itself. After a series of arguments, Tolkien describes the probable final conclusion of the Elf that Eru (God) would in a redemptive fashion enter the world as a Man to cure the evils of Melkor (Satan) and free Men from their original sin. Thus Elvish thought and foresight predict the coming of Christ.
The analysis of the published works The Silmarillion and The Lord of the Rings is important for the study of the influences of Tolkien's faith upon his works. But with the publication of The History of Middle-earth series, we can see first-hand the creative process of Tolkien's works. We can see the secondary fictional works ('Athrabeth Finrod ah Andreth') and philosophical essays that set out definitively Tolkien's attempts to bring his legendarium into a Christian historial framework. Most importantly, we see Tolkien's personal debate over the worth of writing an 'alternate-history' Bible and his ultimate positive answer.