The proverb in the title "Let the punishment fit the crime" is a theory of justice that considers that proportionate punishment is a morally acceptable response to crime and was used as a comic song in the Gilbert and Sullivan production of The Mikado.
The card game of Bridge is an extremely difficult game to master. No way could Agatha teach a complete novice the game in a few hours. At the very least it would take several years to learn and then you would still be a novice.