Remember when you were first starting out learning something new? One of the basic tenets of a wizard profession is that he must communicate with the elementals in the world around him (or her). Now, this isn't as easy as you may assume. He has gone through most of his life and never seen them. Then he is taught to see them but still can't communcate with them. So, the fledgling wizard is introduced to the Oracle Deck.
The basic premise for an Oracle Deck is to be a guide to help through your questions and trials in life. With this knowledge, the magic of the deck helps create a communication link between the wizard and the elemental shown on the deck. Kind of like training wheels. Over time, the language patterns are easy for the wizard to understand so there is no need for the cards to help with a particular creature.
The more cards that are used by the wizard to communicate with different elementals, the more elementals he can speak with. These elementals may or may not help him find the answer to his questions.