Sacrosanctum Concilium

Constitution on the Sacred Liturgy (Vatican II) document summary of Chapter I.

Jesus, at the last supper, invited all the baptized to "Do this in memory of me." christ's real presence is in the Holy Eucharist at mass. Jesus Christ is not just for the baptized - He is for all, so that all may know the true God and Jesus Christ whom he has sent.

Active participation is demanded by the very nature of the liturgy. Such participation by the Christian people, as "a chosen race, a royal priesthood, a holy nation, a redeemed people (1Peter 2:9, cf. 2-4-5) is their right and duty by reason of their baptism."

This chapter goes on to talk about the rites and language used.