The Oracle doubles the effect of temples.
Note that a temple makes 2 citizens content instead of one if the civilization has the Mysticism advance, which allows the Oracle to increase the number of content citizens up to 4.
The combined effect of the advance and the wonder makes temples just as effective as cathedrals but less expensive. .
In ancient Greek religion, an Oracle was a priest or priestess who transmitted a god's response to questions. The Oracle interpreted dreams, the actions of entranced persons, and physical signs found in the entrails of sacrificed animals. The most famous Oracle was the shrine of Apollo at Delphi, located on the slopes of Mt. Parnassos. It was consulted for centuries by Greeks, Romans, and others about public policy and private matters. A priestess called the Pythia would, for a fee, make predictions for the future. These ecstatic pronouncements (oracles) became famous (or infamous) for their ambiguity.