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. (March 2018)
The Old Testament describes how God made his people "a kingdom of priests and a holy nation," and within the twelve tribes of Israel, the tribe of Levi was chosen to be set apart for the liturgical service of offering sacrifice as priests. The priest was understood as a mediator between God and human beings who offers sacrifices and intercedes for the people.
The New Testament depicts Jesus as the "great high priest" of the New Covenant who, instead of offering the ritual animal sacrifices prescribed by the Jewish Law, offers himself on the cross as the true and perfect sacrifice. The Catholic priesthood is a participation in this priesthood of Christ, and therefore traces its origins to Jesus Christ himself. Thus, the New Testament says that as high priest, Jesus has made the Church "a kingdom of priests for his God and Father." All who are baptized are given a share in the priesthood of Christ; that is, they are conformed to Christ and made capable of offering true worship and praise to God as Christians. "The whole community of believers is, as such, priestly."
The ministerial priesthood of Catholic priests and bishops—what most people think of as "the Catholic priesthood"—has a distinct history. This ministerial priesthood is at the service of the priesthood of all believers and involves the direct consecration of a man to Christ through the sacrament of orders, so that he can act in the person of Christ for the sake of the Christian faithful, above all in dispensing the sacraments. It is understood to have begun at the Last Supper, when Jesus Christ instituted the Eucharist in the presence of the Twelve Apostles, commanding them to "do this in memory of me."
The Catholic priesthood, therefore, is a share in the priesthood of Christ and traces its historical origins to the Twelve Apostles appointed by Christ. Those apostles in turn selected other men to succeed them as the bishops (episkopoi, Greek for "overseers") of the Christian communities, with whom were associated presbyters (presbyteroi, Greek for "elders") and deacons (diakonoi, Greek for "servants"). As communities multiplied and grew in size, the bishops appointed more and more presbyters to preside at the Eucharist in place of the bishop in the multiple communities in each region. The diaconate evolved as the liturgical assistants of the bishop and his delegate for the administration of Church funds and programmes for the poor. Today, the rank of "presbyter" is typically what one thinks of as a priest, although technically both a bishop and a presbyter are "priests" in the sense that they share in Christ's ministerial priesthood and offer sacrifice to God in the person of Christ.