Upvote:2
The Old Testament priesthood is a foreshadow of the New Testament priesthood, but many features are different; the word for OT/pagan priest and for NT priest is also different in some languages including Greek and Latin.
The OT Levite priesthood was tied to bloodline of Aron and their role was to sacrifice animals and other offerings in the Temple. These features of priesthood were abandoned with the sacrifice of Jesus.
The ministerial priesthood (and common priesthood shared by all baptised too) is derived from the priesthood of Christ. Similarly to several levels of discipleship of Jesus' followers in the Gospels (Twelve/ Seventy/ the crowds), there are different levels of participation of Christ's priestly authority.
The ministerial priests' role is to serve people in the place of Christ, especially while performing the sacraments. As a sacrifice was a definition feature of Levite priesthood, sacrament is a crucial point of Catholic ministerial priesthood.
As there were only the Twelve in the Upper Room while Jesus said about the Eucharist: "Do it in the remembrance of me!", we believe that the Twelve and their successors (the bishops and priests) have the power to perform the visible part of the miracle of transsubstantiation (about the other Christians and this priestly power, there's nothing in the Bible, but tradition said "no").
The same is true about the confession and most other sacraments - they were given to the twelve, so only those ordained to do so have the power.
I found an article on this topic; I used it as my primary source.
Upvote:5
They are obviously not re-sacrificing Christ when they say the Mass
It's true enough that they are not re-sacrificing Christ. But in a mystical way the Catholic priest acts in persona Christi to offer, in an unbloody way, the very same sacrifice that was offered in a bloody way on Calvary. Here is the modern Catholic Catechism (paragraph 1367), quoting the 16th-century Council of Trent (my emphases):
The sacrifice of Christ and the sacrifice of the Eucharist are one single sacrifice: "The victim is one and the same: the same [Christ] now offers through the ministry of priests, Who then offered Himself on the cross; only the manner of offering is different."
Thus a principal point of having priests, in the Catholic Church, is to continually make the unique, unrepeatable sacrifice of Calvary mystically present to us here and now. Our priests, like Christ himself, are of the order of Melchizedek, not the order of Aaron. Indeed there is in a sense only the priesthood of Christ -- as St. Thomas Aquinas says (and the modern Catechism quotes, paragraph 1545):
Only Christ is the true priest, the others being only his ministers