Mediator Dei §49

⁴⁹ From time immemorial the ecclesiastical hierarchy has exercised this right in matters liturgical. It has organized and regulated divine worship, enriching it constantly with new splendor and beauty, to the glory of God and the spiritual profit of Christians. What is more, it has not been slow - keeping the substance of the Mass and sacraments carefully intact - to modify what it deemed not altogether fitting, and to add what appeared more likely to increase the honor paid to Jesus Christ and the august Trinity, and to instruct and stimulate the Christian people to greater advantage.