In Civilization and Civilization II, the temple is a city improvement that makes discontented citizens content. Since a city with discontented citizens goes into rebellion and becomes totally non-productive, building temples quickly becomes a neccesity.
A temple requires only the simple civilization advance of ceremonial burial and a relativly small amount of resource shields to build. However, often it must be built so early in the game that cities don't have enough shields to build them quickly.
While there are different strategies for playing Civ, with different emphasis on what structures to build in each, at higher levels of the game, building temples quickly is a neccesity, independent of what strategy you choose to pursue afterwords.