70 Young candidates for the priesthood should be convinced that they cannot follow their difficult way without a special type of asceticism proper to themselves and more demanding than that which is required of the other faithful. It will be a demanding asceticism but not a suffocating one which consists in the deliberate and assiduous practice of those virtues which make a man a priest: self-denial in the highest degree—an essential condition if one would follow Christ; (118) humility and obedience as expressions of internal truth and of an ordered liberty; prudence, justice, courage and temperance—virtues without which it is impossible for true and profound religious life to exist; a sense of responsibility, fidelity and loyalty in the acceptance of one's obligations; a balance between contemplation and action; detachment and a spirit of poverty, which will give tone and vigor to evangelical freedom; chastity, the result of a persevering struggle, harmonized with all the other natural and supernatural virtues; a serene and secure contact with the world to whose service the young man will dedicate himself for Christ and for His kingdom. In such a way the aspirant to the priesthood will acquire, with the help of a divine grace, a strong, mature and balanced personality, a combination of inherited and acquired qualities, harmony of all his powers in the light of the faith and in intimate union with Christ, whom he has chosen for himself and for the ministry of salvation to the world.
Source: Sacerdotalis Caelibatus (Vatican.va)