Prosper of Aquitaine, a disciple of St. Augustine in the church’s early efforts to clarify its faith coined a phrase in Latin that is often condensed and reads, lex orandi, lex credendi.  Loosely translated the Latin (it is often said) means, “the law of praying is the law of believing” or – to put it more directly,

Source: Praying, Believing and Open Communion | Frederick Schmidt