Arbitration is a way for players to begin to make more money towards the end of their rookie contract and the St. Louis Cardinals have always been great at reaching agreements with their players. The arbitration process gives the players a voice in their salary and the agreed price is usually reflective of their performance in the year prior.
It is a semi complicated process, but in short, if the team and the player do not agree to a deal before the deadline, they go to court for a judge to decide what a player should make.