CCC 1566

"It is in the Eucharistic cult or in the Eucharistic assembly of the faithful (synaxis) that they exercise in a supreme degree their sacred office; there, acting in the person of Christ and proclaiming his mystery, they unite the votive offerings of the faithful to the sacrifice of Christ their head, and in the sacrifice of the Mass they make present again and apply, until the coming of the Lord, the unique sacrifice of the New Testament, that namely of Christ offering himself once for all a spotless victim to the Father." From this unique sacrifice their whole priestly ministry draws its strength.