“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.
It is, therefore, the sacrament of the apostolic ministry. It includes three degrees: episcopate, presbyterate, and diaconate”. (Catechism of the Catholic Church, 1536).
“No one has a right to receive the sacrament of Holy Orders. Indeed, no one claims this office for himself; it is received by a call from God (cf. Heb 5:4). He who believes he recognizes the signs of God’s call to the ordained ministry must humbly submit his desire to the authority of the Church, which has the responsibility and the right to call someone to receive Orders. Like every grace, this sacrament can only be received as an unmerited gift.” (Catechism of the Catholic Church, 1578).