"The whole plan of singing should be constituted not to give empty pleasure to the ear, but in such a way that the words be clearly understood by all. And thus the hearts of listeners be drawn to desire of heavenly harmonies in the contemplation of the joys of the Blessed. They shall also banish from church all music that contains whether in the singing or in the organ playing things that are lascivious or impure."
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This comes from the Council of Trent (1545-1563), specifically the Canon on Music to be used for the Mass.