The one he used most often, and is not a concept limited merely to Judeo-Christian theology, is prophecy (telling of the future from the deep past). In this case he uses "legends" and "songs" to pass forward the "prophecies".
And at this point in the story, with Aragorn's decision being critical to what comes after, the role of "prophecy" may be decisive: Aragorn knew intimately all of the prophecies about the King returning to Gondor (this in itself appears to be something based on Judeo-Christian forms) to claim Kingship from the Steward, and how only the rightful King could marshal the Army of the Dead (which was, for those with "eyes" to see it, a test of his rightful claim). And Aragorn knew that is was he who was to make the claim -- though it would have to be very "delicately" handled. Many others in the story, Elrond, Evenstar, Galadriel, Gandalf -- and probably Saruman and Sauron -- were also aware of the prophecies and that they pointed to Aragorn.
I think Aragorn's intimate knowledge of the prophecies and their application to himself was at least one of the reasons he made this particular choice (to go after Merry and Pippin). He knew more about his final role in all this than we are led to believe at this point in the story.
P.S. sorry for the long post -- it didn't start out that way...