Holy Orders is the sacrament through which 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. It includes three degrees: episcopate, presbyterate, and diaconate. St. Paul said to his disciple Timothy: “I remind you to rekindle the gift of God that is within you through the laying on of my hands,” and “If any one aspires to the office of bishop, he desires a noble task.” To Titus he said: “This is why I left you in Crete, that you amend what was defective, and appoint presbyters in every town, as I directed you.”
The whole Church is a priestly people. Through Baptism all the faithful share in the priesthood of Christ. This participation is called the “common priesthood of the faithful.” Based on this common priesthood and ordered to its service, there exists another participation in the mission of Christ: the ministry conferred by the sacrament of Holy Orders, where the task is to serve in the name and in the person of Christ the Head in the midst of the community.
The ministerial priesthood differs in essence from the common priesthood of the faithful because it confers a sacred power for the service of the faithful. The ordained ministers exercise their service for the People of God by teaching (munus docendi), divine worship (munus liturgicum) and pastoral governance (munus regendi). – Catechism of the Catholic Church 1536, 1590-1592.