Thank you for that. It was interesting as I've not heard of this before. It resonated with the part of me that BELIEVES in Judaism, though I'm a practicing Catholic. I believe you can't successfully be Christian if you don't believe in Judaism.
However -- when did the other tribes besides the Levites become priests? Are Levites Jews? Or are Jews only of the tribe of Judah, and possibly Benjamin?
You're misunderstanding. Israel is a "priestly people" to the rest of the world. This is completely distinct from the Levitical priesthood.
Just as there is a distinction between Kohanim, Leviyim, and Yisra'elim among the Jews, so there is a distinction between the Nation of Israel and the Nations of the World. The world is full of distinctions, and everyone has his own assigned role.