Charles wants to make a mark on the world that will last long after he is gone.
Of the last four seasons, this is by far my favorite episode - it has lots of elements that work together and are thoughtfully executed. That there are no impossible historical inaccuracies is a bonus (other than Minneapolis is now about as easy to reach by wagon as Sleepy Eye once was).
I can really believe that Charles Ingalls, a man who had become a talented woodworker, would want to leave a legacy of his work at an age that he plays in this episode. The scenes of Jack Prescott bemoaning that he never did are good and his death by heart attack is emotional. It's also realistic that Charles' dream is not realized because his work is stolen and mass-produced by a large furniture manufacturer - introducing the fact that bad luck and competition, often "unfair", can spoil a driven person's dreams. The secondary story of Albert firing a handyman hired to do the farmwork is also well-done, and though James has literally no dialog, this is a rare example of how the newest "blended" Ingalls family could have worked together.
Tying a piece of Charles Ingalls crafted furniture into a "modern" flea market is just a nice added touch and lends an added emphasis to the main theme - people's longing to leave a record that persists beyond the short lifespan of the individual.