CCC 1534 - Two sacraments, Holy Orders and Matrimony, are directed towards the salvation of others; if they contribute as well to personal salvation, it is through service to others that they do so. They confer a particular mission in the Church and serve to build up the People of God.
CCC 1536: Holy Orders are 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.
The ministerial priesthood is a means by which Christ unceasingly builds up and leads his Church. For this reason it is transmitted by its own sacrament, the sacrament of Holy Orders. In the ecclesial service of the ordained minister, it is Christ himself who is present to his Church as Head of his Body, Shepherd of his flock, high priest of the redemptive sacrifice and Teacher of the Truth. Priesthood is in the strict sense of the term a ‘service’; it was instituted for the good of men and the communion of the Church. An Ordained priest is called to consecrate himself with undivided heart to the Lord and to “the affairs of the Lord,” to give himself entirely to God and to men. He acts as a representative of Christ, Head of the Church, in his triple office of priest, prophet and king. The sacrament of Holy Orders confers an indelible spiritual character and cannot be repeated or conferred temporarily. (see CCC 1547, 1548, 1551, 1579, 1581 and 1582)