We're not talking about the Silmarillion, we're talking about the Lord of the Rings. And in the trilogy, there is no reference to God. The Silmarillion was written later and never finished in Tolkien's lifetime.
Gandalf, in his confrontation with Balrog in the Mines of Moria, refers to himself as "the Servant of the Secret Fire." The Secret Fire is the Holy Spirit, according to Tolkien.
Sorry, I can't buy this. The only reference to God is "the secret fire"? And somehow this makes the work all Catholic? This sounds totally pagan, which would be in keeping with Tolkien's sources in Norse mythology.
When the interviewers asked him who the God in the trilogy was, Tolkien said: "The one, of course! The book is about the world that God created - the actual world of this planet."
If the world of LoR is supposed to be our world, then all the more reason to make the absence of God inexcusable. Where, by the way, are Adam and Eve in the story? What about the condemnation of poly-genism that came out during the very time that Tolkien was writing the books? This is absolutely unacceptable from a Catholic perspective.
Please read the third chapter of Bradley Birzers' book, J.R.R. Tolkien's Sanctifying Myth before repeating such a statement.
If I need to read someone else's explanation before understanding where God fits into the story, then that is just perfect confirmation of the fact that it is not there in the text. I've read others besides Joseph Pierce promoting this theory, and none of them are credible.
You cannot separate the two. You do not have to read the Silmarillion to understand the Lord of the Rings. But, by doing so, you get a clearer picture of Tolkien's intent.