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.
Catechism of the Catholic Church 1536
As he passed by the Sea of Galilee He saw Simon and his brother Andrew casting their nets into the sea; they were fishermen. Jesus said to them, “Come after me, and I will make you fishers of men.” And they left their nets and followed Him. (Mark 1:16-18)