וְעַתָּ֗ה קְח֤וּ לָכֶם֙ שְׁנֵ֣י עָשָׂ֣ר אִ֔ישׁ מִשִּׁבְטֵ֖י יִשְׂרָאֵ֑ל אִישׁ־אֶחָ֥ד אִישׁ־אֶחָ֖ד לַשָּֽׁבֶט׃
Now therefore take you twelve men out of the tribes of Israel, for every tribe a man.
Rashi on Joshua
Take for yourselves twelve men. Prepare them to be available to fulfil that which I will command them when you finally cross the Jordan.