“Since the Church has received from Christ her Founder the office of safeguarding the sanctity of divine worship, it is certainly incumbent upon her, while leaving intact the substance of the Sacrifice and the sacraments, to prescribe ceremonies, rites, formulae, prayers and chant for the proper regulation of that august public ministry, whose special name is “Liturgy”, as being the eminently sacred action”

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Pope Pius XI

Divini Cultus

(translation from here)