What does Joshua 18:7 mean?

'The Levites don’t get a share, because their job is to serve God as priests. Gad, Reuben, and half of Manasseh already got their land east of the Jordan, given by Moses.' Joshua 18:7 - Modern Text Bible

(Joshua reminds them that the Levites’ inheritance is their priestly role, and some tribes already have land on the other side of the river.)