The stout man in a red sweater taught Buck to respect the man holding the club. Thus, the club is not only used to inflict pain but also serves as a symbol of authority.
The lesson was driven home to Buck: a man with a club was a lawgiver, a master to be obeyed, though not necessarily conciliated.
The four men carrying the crate are afraid that the man in the red sweater will be torn to pieces given Buck’s dangerous state. However, the man lets Buck out of the crate, showing no fear. The dog lunges forward to attack but is hit by the club. Buck becomes even more aggressive and tries to attack repeatedly, but each time the club lands, causing serious pain. Eventually, Buck is struck senseless and learns the painful law of the club. The man later gives Buck some water and chunks of meat, completing the conditioning.
The lesson is also relevant to human beings because it demonstrates the need to respect existing laws and the authority of those mandated to enforce the laws. Society is also conditioned on the basis of punishment and reward. People are punished for breaking the law and rewarded when they uphold the law.