Why did the man in the red sweater take Buck out his crate and what lesson did he teach Buck?

When the train is unloaded, a man in a red sweater approaches the crate, as four other men look on. The man carries a hatchet and a club; first, he uses the hatchet to break open Buck's crate. Anxious to loose his pent up fury, Buck leaps at him and is struck by a club, a new and horrible experience. Mad fury drives Buck, but each time he rushes the man, he is struck again, until he is beaten and bloodied. At last he can no longer rise. The red sweater genially tells him to mind his place, pats his head, and provides him with meat and water. Buck is beaten, not broken . He has learned not to fight a club. Other dogs arrive and undergo the same process. Buck respects the red sweater, but he is too proud to seek the man's affection, as other dogs do.