G-d told Moses to tell Aaron, "Behold, I have joyfully given you the charge of safeguarding My raised-offerings from defilement. By giving you this responsibility I have thus given you all the holy things that the Israelites give to Me. I give them to you as a sign of eminence and as an eternal portion of your descendants.
Bamidbar 18:8
Although the physical priesthood was reserved for the descendants of Aaron, the spiritual priesthood is accessible to all. G-d calls the entire Jewish people "a kingdom of priests." As Maimonides explains, "Any human being whose spirit moves him - and whose intellect has motivated him - to distinguish himself by standing before G-d, serving Him, and knowing Him... has become sanctified like the Holy of Holies...and will be granted all of his physical needs, just as they were provided for the priests and Levites.
In other words, when we recognize the purpose of our lives-to serve G-d -and dedicate ourselves to accomplishing it, we are assured of the best of everything, material and spiritual, at all times.
--From Kehot's
Chumash Bamidbar