Catholics believe that the one true priest is Jesus Christ, but that in His earthly life, Jesus gave a share in his priesthood to the 12 apostles. The apostles in turn ordained other men to share in the priesthood of Christ (2 Timothy 1:6), and the priesthood has thus been handed on through the authority of the Church for two millennia.
The priesthood is not a position of power, but of service (Matthew 20:25-28, John 13:2-20). The modern, secular world tends to view the priesthood from the perspective of politics and power, but Jesus specifically rejects such a view in the Gospels.
Priests carry on the ministry of Jesus through the sacraments and the preaching of the Gospel, they are called to strengthen the people of God so they might be the light of the world.
It is through Holy Orders that “the mission entrusted by Christ to his apostles continues to be exercised in the Church until the end of time: thus it is the sacrament of apostolic ministry.” (CCC 1536)
From Jesus’ conception until his resurrection he was filled with the Holy Spirit, thus established by God the Father as our high priest and remains our high priest. Ordination to the priesthood is always a call and gift from God. Those who seek priesthood respond generously to God’s call using the word’s of the prophet, “Here I am, send me” (Is 6:8). This call from God can be recognized and understood from the daily signs that disclose his will to those in charge of discerning the vocation of the candidate. – United States Catholic Catechism for Adults.