"For as often as you shall eat this bread, and drink the chalice, you shall shew the death of the Lord, until he come. Therefore whosoever shall eat this bread, or drink the chalice of the Lord unworthily, shall be guilty of the body and of the blood of the Lord. But let a man prove himself: and so let him eat of that bread, and drink of the chalice. For he that eateth and drinketh unworthily, eateth and drinketh judgment to himself, not discerning the body of the Lord. Therefore are there many infirm and weak among you, and many sleep."
~1 Corinthians 11: 26-30
It is the whole community, the Body of Christ united with its Head, that celebrates. "Liturgical services are not private functions but are celebrations of the Church which is 'the sacrament of unity,' namely, the holy people united and organized under the authority of the bishops. Therefore, liturgical services pertain to the whole Body of the Church. They manifest it, and have effects upon it. But they touch individual members of the Church in different ways, depending on their orders, their role in the liturgical services, and their actual participation in them." For this reason, "rites which are meant to be celebrated in common, with the faithful present and actively participating, should as far as possible be celebrated in that way rather than by an individual and quasi-privately."
The celebrating assembly is the community of the baptized who, "by regeneration and the anointing of the Holy Spirit, are consecrated to be a spiritual house and a holy priesthood, that through all the works of Christian men they may offer spiritual sacrifices." This "common priesthood" is that of Christ the sole priest, in which all his members participate:
Mother Church earnestly desires that all the faithful should be led to that full, conscious, and active participation in liturgical celebrations which is demanded by the very nature of the liturgy, and to which the Christian people, "a chosen race, a royal priesthood, a holy nation, a redeemed people," have a right and an obligation by reason of their Baptism.