Pope Pius XII (1939-58) was a great pope in many ways, but he holds an especially important place in the rediscovery of the liturgy. The Fathers of Vatican II, in fact, proclaimed their document on the liturgy to be “the last will and testament of Pius XII.”
Here, in his monumental 1947 encyclical on the liturgy, Mediator Dei, he explains what “active participation in the liturgy” really means, and how essential it is to our relationship with Christ.
The cooperation of the faithful is required so that sinners may be individually purified in the blood of the Lamb. For though, speaking generally, Christ reconciled by His painful death the whole human race with the Father, He wished that all should approach and be drawn to His cross, especially by means of the sacraments and the eucharistic sacrifice, to obtain the salutary fruits produced by Him upon it. Through this active and individual participation, the members of the Mystical Body not only become daily more like to their divine Head, but the life flowing from the Head is imparted to the members, so that we can each repeat the words of St. Paul, “With Christ I am nailed to the cross: I live, now not I, but Christ liveth in me.”
We have already explained sufficiently and of set purpose on another occasion, that Jesus Christ “when dying on the cross, bestowed upon His Church, as a completely gratuitous gift, the immense treasure of the redemption. But when it is a question of distributing this treasure, He not only commits the work of sanctification to His Immaculate Spouse, but also wishes that, to a certain extent, sanctity should derive from her activity.”
The august sacrifice of the altar is, as it were, the supreme instrument whereby the merits won by the divine Redeemer upon the cross are distributed to the faithful: “as often as this commemorative sacrifice is offered, there is wrought the work of our Redemption.” This, however, so far from lessening the dignity of the actual sacrifice on Calvary, rather proclaims and renders more manifest its greatness and its necessity, as the Council of Trent declares.
Its daily immolation reminds us that there is no salvation except in the cross of our Lord Jesus Christ and that God Himself wishes that there should be a continuation of this sacrifice “from the rising of the sun till the going down thereof,” so that there may be no cessation of the hymn of praise and thanksgiving which man owes to God, seeing that he required His help continually and has need of the blood of the Redeemer to remit sin which challenges God’s justice.
It is, therefore, desirable, Venerable Brethren, that all the faithful should be aware that to participate in the eucharistic sacrifice is their chief duty and supreme dignity, and that not in an inert and negligent fashion, giving way to distractions and day-dreaming, but with such earnestness and concentration that they may be united as closely as possible with the High Priest, according to the Apostle, “Let this mind be in you which was also in Christ Jesus.” And together with Him and through Him let them make their oblation, and in union with Him let them offer up themselves.
-Pope Pius XII, Mediator Dei