5 And firstly We urge and exhort you concerning the preparation and welfare of the clergy. For the clergy are like an army, which, as they obey the laws and perform their duties so that they may be of service to the Christian multitude under the authority of the bishops, will bring honour and stability to public affairs in proportion to their number and discipline. Wherefore this has always been the first care of the Church that she should choose and bring up to the priesthood those young men, whose dispositions and desires afford a hope that they will persevere in the ministry of the Church ( Conc. Trid., Sess. xxiii., de reform cxviii .), and again, that the young men should have been educated from their early years in piety and religion, before evil habits have gained possession of them as young men, ( Conc. Trid., Sess. xxiii., de reform cxviii. ), and for them she founded proper seats of training and seminaries, and laid down rules full of wisdom, especially in the holy Council of Trent ( ibid .), so that this college of the ministers of God might be a perpetual seminary ( ibid .). In several places indeed, certain laws are in force which, if they do not stop, yet hinder the clergy in their training and discipline. We deem that it behoves Us now as at other times openly to speak Our mind on this matter, which is of the greatest possible interest, and to preserve the holy law of the Church inviolate by every means in Our power. For indeed the Church, as a body, which is by its nature perfect, has an inalienable right of ordering and instructing its own forces, hurtful to none, helpful to many in that kingdom of peace which Jesus Christ founded upon earth for the salvation of the human race.
Source: Officio Sanctissimo (Vatican.va)