Notice....It wasn't the qualifications, or education level of Joshua, that God pointed to...
Let the LORD, the God of the spirits of all flesh,
set a man over the congregation,
...that the congregation of the LORD be not as sheep which have no shepherd.
And the LORD said unto Moses,
Take thee Joshua the son of Nun,
a man in whom is the spirit,
and lay thine hand upon him;
Numbers 27:16-18