Christianity in Tolkien's Work

Tolkien, a language professor at Offord and the author of The Lord of the Rings, was a strong Christian. Many people draw connections between The Lord of the Rings and his faith, even though Tolkien himself quite clearly said that the books were not an allegory of any kind.

I cordially dislike allegory in all its manifestations, and always have done so since I grew old and wary enough to detect its presence. - Tolkien Gateway

 However, when he did this he made a difference between the words allegory and applicability. 

I think that many confuse 'applicability' with 'allegory'; but the one resides in the freedom of the reader, and the other in the purposed domination of the author. - Tolkien Gateway

Tolkien thought that allegory was the forceful pushing of the author's views onto the reader. He also thought that applicability was the reader drawing connections between the themes of the narrative and real-life lessons (For example, someone might take the scene where Frodo had mercy on Gollum and did not kill him and conclude that we should be merciful in real life.). 

The Lord of the Rings is, therefore, not an allegory, but Tolkien clearly intended us to apply the themes and morals he presented in the story to our own lives. The Messiah Comes to Middle-Earth by Phillip Ryken does this by finding the elements of Priest, Prophet, and King in the story and using them as an illustration of Jesus being our own Prophet, Priest, and King, helping us understand these roles better.