Why is the Cratchit's older son looking for a new job in the Christmas carol?

A the time (1843) in Britain work was scarce. Many companies would employ child labour to save money. Apprentiships were scarce and often nowhere near the home of the person applying. Bob Cratchit had seen an opportunity for his son Peter which could, if he were successful a full five-and-sixpence weekly in income. The jobs title is never explained in the original story except to say that "his sisters laughed at the thought of Peter being a man of business."