For if the sacred liturgy holds the first place in the life of the Church, the Eucharistic Mystery stands at the heart and center of the liturgy, since it is the font of life by which we are cleansed and strengthened to lie not for ourselves but for God, and to be united in love among ourselves. To make evident the indissoluble bond which exists between faith and devotion, the Fathers of the council, confirming the doctrine which the Church has always held and taught and which was solemnly defined by the Council of Trent, determine to introduce their treatise on the Most Holy Mystery of the Eucharist with the following summary of truths:
In these words are highlighted both the sacrifice, which pertains to the essence of the Mass which is celebrated daily, and the sacrament in which the faithful participate in Holy Communion by eating the Flesh of Christ and drinking His Blood, receiving both grace, the beginning of eternal life, and the medicine of immortality. According to the words of Our Lord: The man who eats my flesh and drinks my blood enjoys eternal life, and I will raise him up at the last day.
Therefore we earnestly hope that the restored sacred liturgy will bring forth abundant fruits of eucharistic devotion, so that the Holy Church, under this saving sign of piety, may make daily progress toward perfect unity and may invite all Christians to a unity of faith and of love, drawing them gently, thanks to the action of divine grace. (Papal Encyclical, Mysterium Fidei, 1965).