In the book Bronze Bow, why must Joel have an occupation?

In Chapter 1, after Joel and Malthace run into Daniel on the mountain, Joel asks Daniel what he does all the time. Daniel tells Joel that he hunts and works at his forge in the cave. Daniel then asks Joel what his trade is, and Joel tells him that he his going to be a rabbi, but is studying sandal-making too. Joel mentions that he could earn a living making sandals, but is not very good at his trade. Later on in Chapter 5, Daniel sits down to eat dinner with Hezron and his family. Hezron asks Daniel if he follows his father's trade. Daniel says "no," and explains that he was bound to Amalek, the ironsmith. Hezron comments, "it is necessary for every boy to learn a trade," and goes on to say that he was a sandal maker, and Joel follows the same trade (Speare 64). One can surmise that rabbis did not earn a significant amount of income from their priestly duties, and they were forced to learn other trades, such as sandal-making in order to make ends meet. Joel is a rabbi in training and needs to rely on another skill set in order to earn a living.