Frodo and Jesus
The Aragorn:Boromir::David:Jonathan equation is workable for the movies, but not the books, where Aragorn and Boromir cannot be construed as soul-mates.
I'm pretty sure I've seen professionally-published Tolkien criticism discussing how Aragorn, Frodo, Gandalf, and Sam are each different aspects of the heroic, and how each also has Christ-like qualities. Tolkien's world is pre-Christian -- that is, he thought of it as a world in which Christ *will* come, but hasn't yet -- so each of his heroes is a prefiguration of Christ: Aragorn for kingship, Frodo for sacrifice, Gandalf for resurrection, and Sam for service ... and it now occurs to me that this four-way split mirrors the traditional characterization of the Four Evangelists.
I'm talking about the traditional symbology where the Gospel of Matthew is symbolized by a (winged) man, for Christ's human nature (=Sam), Mark is a lion, for Christ's kingship (=Aragorn), Luke is a bull or ox, for sacrifice (=Frodo), and John as a eagle, for Christ's mystic glory (=Gandalf).
My guess (based on a deep not to say obsessive knowledge of Tolkieniania) is that Tolkien did notmake these parallels consciously, but that he was used to thinking this way. Just as the author of Revelation got the four animals from Ezekiel and the Church Fathers matched them up to the four Gospels, the Gospels and their traditional symbols were part of the furniture of Tolkien's mind.
Do modern American Evangelicals use this symbology? I was raised Catholic with a lot of art history, so this is very familiar to me, too.