18 But your chief cares and thoughts, Venerable Brethren, must have for their object the due appointment of fitting ministers of God. For if it be the office of Bishops to use very much labour and zeal in properly training the whole of their youth, they ought to spend themselves far more on the clerics who are growing up as the hope of the Church, and are to be some day sharers in the most sacred duties. Indeed, grave reasons, common to all times, demand in priests many and great graces; but this time in which we live demands that they should be even more and greater. In truth the defence of the Catholic Faith, in which the industry of priests ought specially to be employed, and which is in these days so very necessary, demands no common nor ordinary learning, but that which is recondite and varies; which embraces not only sacred, but even philosophical studies, and is rich in the treatment of physical and historical discoveries. For the error which has to be eradicated is multiform, and saps all the foundations of Christian wisdom; and very often a battle has to be waged with adversaries well prepared, pertinacious in disputing, who astutely draw confirmation from every kind of science. Similarly, since in these days there is great and far extended corruption of morals, there is need in priests of singular excellence of virtue and constancy. They can by no means avoid associating with men; by the very duties of their office, indeed, they are compelled to have intimate relations with the people; and that in the midst of cities where there is hardly any lust that has not permitted and unbridled license. From which it follows that virtue in the clergy ought at this time to be strong enough peacefully to guard itself, and both conquer all the blandishments of desire and securely overcome dangerous examples. Besides a paucity of clerics has everywhere followed the laws which have been enacted to the injury of the Church, so plainly, that it is necessary for those who by the grace of God are being trained to Holy Orders, to give double attention, and by increased diligence, zeal, and devotion to compensate for the sparse supply. And, indeed, they cannot do this advantageously unless they possess a soul resolute of purpose, mortified, incorrupt, ardent with charity, ever prompt and quick in undertaking labours for the salvation of men. But for such tasks a long and diligent preparation must be made; for one is not accustomed to such great things easily and quickly. And they indeed will pass their time in the priesthood holily and purely, who have exercised themselves in this way from their youth, and have so advanced in discipline that they seem not so much to have been instructed to those virtues, of which We have spoken, as to have been born to them.
Source: Etsi Nos (Vatican.va)