We have Mass to worship and to receive God’s grace, to unify with him and with other worshipers through the sacrament of the Eucharist. As a sacrament, it is that Jesus himself acting through the Eucharist, and supplies all the graces we derive from it.
At Mass we are able to stand mystically at the foot of the cross and witness for ourselves the same self-sacrifice of Jesus, in an unbloody manner.
Mass is a celebration of this sacrifice. It is the active participation of all that come together in the place of worship. We do not come to Mass simply to receive something passively or to watch a show; we come as participants embracing the grace Christ pours out for us shed by his own blood on the cross.