The Shevet of Levi doesn’t have a portion in Eretz Yisroel. They live off the terumah and ma’aser given to them from the rest of the Jewish people. They have a special promise from Hashem that He will make sure they will be taken care of.
The Ramba”m takes this further by saying that this promise is not only given to Shevet Levi, but anyone who dedicates themselves to properly serving Hashem and stops worrying about worldly troubles is given this promise.
The 24 gifts of kehuna were given to the Kohanim specifically because they weren’t involved in anything besides the avodah. They were given them without doing any effort at all to receive them.
So to anyone who wants to be dedicated to growing in their avodah will be given all that they need without any effort.