Sacrosanctum Concilium §50

⁵⁰ The rite of the Mass is to be revised in such a way that the intrinsic nature and purpose of its several parts, as also the connection between them, may be more clearly manifested, and that devout and active participation by the faithful may be more easily achieved. For this purpose the rites are to be simplified, due care being taken to preserve their substance; elements which, with the passage of time, came to be duplicated, or were added with but little advantage, are now to be discarded; other elements which have suffered injury through accidents of history are now to be restored to the vigor which they had in the days of the holy Fathers, as may seem useful or necessary.