40 Only to the apostles, and thenceforth to those on whom their successors have imposed hands, is granted the power of the priesthood, in virtue of which they represent the person of Jesus Christ before their people, acting at the same time as representatives of their people before God. This priesthood is not transmitted by heredity or human descent. It does not emanate from the Christian community. It is not a delegation from the people. Prior to acting as representative of the community before the throne of God, the priest is the ambassador of the divine Redeemer. He is God's vice-gerent in the midst of his flock precisely because Jesus Christ is Head of that body of which Christians are the members. The power entrusted to him, therefore, bears no natural resemblance to anything human. It is entirely supernatural. It comes from God. "As the Father hath sent me, I also send you . . . he that heareth you heareth me . . . go ye into the whole world and preach the gospel to every creature; he that believeth and is baptized shall be saved."
Source: Mediator Dei (Vatican.va)