29 It is an unquestionable fact that the work of our redemption is continued, and that its fruits are imparted to us, during the celebration of the liturgy, notable in the august sacrifice of the altar. Christ acts each day to save us, in the sacraments and in His holy sacrifice. By means of them He is constantly atoning for the sins of mankind, constantly consecrating it to God. Sacraments and sacrifice do, then, possess that "objective" power to make us really and personally sharers in the divine life of Jesus Christ. Not from any ability of our own, but by the power of God, are they endowed with the capacity to unite the piety of members with that of the head, and to make this, in a sense, the action of the whole community. From these profund considerations some are led to conclude that all Christian piety must be centered in the mystery of the Mystical Body of Christ, with no regard for what is "personal" or "subjective, as they would have it. As a result they feel that all other religious exercises not directly connected with the sacred liturgy, and performed outside public worship should be omitted.
Source: Mediator Dei (Vatican.va)