Whilst this encyclical doesnt at first sight appear to be entirely relevant to those discerning Vocations, it has some very relevant and apt observations on the priesthood and those aspiring to it, I've quoted the relevant sections below:
"On the education of the Clergy
From the beginning of our Pontificate having gravely considered the serious conditions of society, we are not slow to recognize, as one of the most urgent duties of the Apostolic office, that of devoting a most special care to the education of the clergy.
We see in fact that all our designs to bring about a restoration of Christian life among our people, would be in vain if in the ecclesiastical state the sacerdotal spirit was not preserved intact and vigorous. This we have not ceased to do, as far as was possible to us, both with institutions and writings directed to that end. And now a particular solicitude regarding the clergy of Italy moves us, venerable brethren, again to treat on this subject of so great importance. It is true, beautiful and continued testimonies have been shown of learning, piety and zeal, among which we are glad to praise the alacrity with which, seconding the impulse and direction of their bishops, they cooperate in that Catholic movement which we have so much at heart. We cannot altogether, however, hide the preoccupation of our soul at seeing for some time past a certain desire of innovation insinuating itself here and there, as regards the constitution as well as the multiform actions of the sacred ministry. Now it is easy to foresee the grave consequences which we should have to deplore if a speedy remedy were not applied to this innovating tendency.
Therefore, in order to preserve the Italian clergy from the pernicious influences of the times, we deem it opportune, venerable brethren, to recall in this our letter, the true and invariable principles that should regulate ecclesiastical education and the entire sacred ministry. The Catholic priesthood-divine in its origin, supernatural in its essence, immutable in its character, is not an institution that can accommodate itself with ease to human systems and opinions. A participation of the eternal priesthood of Jesus Christ, it must perpetuate even to the consummation of ages the same mission that the Eternal Father confided to His Incarnate Word: "Sicut misit me Pater, et ego mitto vos."' To work the eternal salvation of souls will always be the great commandment of which it must never fall short, as to faithfully fulfil it, it must never cease to have recourse to those supernatural aids and those divine rules of thought and of action which Jesus Christ gave His Apostles when He sent them throughout the whole world to convert the nations to the Gospel. Therefore St. Paul in his letters reminds us that the priest can never be anything but the legate, the minister of Christ, the dispenser of His mysteries, and he represents him to us as dwelling in a high place as a mediator between heaven and earth, to treat with God, about the supreme interests of the human race, which are those of everlasting life. The idea that holy books give us of the Christian priesthood, is that it is a supernatural institution superior to all those of earth, and as far separated from them as the divine is from the human.
This same high idea is clearly brought out by the works of the Fathers, the laws of the Roman Pontiffs, and the Bishops, by the decrees of the Councils, and by the unanimous teaching of the Doctors and of the Catholic schools. Above all, the tradition of the Church with one voice proclaims that the priest is another Christ, and that the priesthood though exercised on earth merits to be numbered among the orders of heaven; because it is given to them to administer things that are wholly celestial and upon them is conferred a power that God has not trusted even to the angels; a power and ministry which regard the government of souls, and which is the art of arts.Therefore, education, studies, customs, and whatever comprises the sacerdotal discipline have always been considered by the Church as belonging entirely to herself, not merely distinct, but altogether separate from the ordinary rules of secular life. This distinction and separation must, therefore, remain unaltered, even in our own times, and any tendency to accommodate or confound the ecclesiastical life and education with the secular life and education must be considered as reproved, not only by the traditions of Christian ages, but by the apostolic doctrine itself and the ordinances of Jesus Christ.
Certainly in the formation of the clergy and the sacerdotal ministry, it is reasonable that regard should be had to the varied conditions of the times. Therefore we are far from rejecting the idea of such changes as would render the work of the clergy still more efficacious in the society in which they live, and it is for that reason that it has seemed necessary to us to promote among them a more solid and finished culture, and to open a still wider field to their ministry; but every other innovation which could in any way prejudice what is essential to the priest must be regarded as altogether blameworthy. The priest is above all constituted master, physician and shepherd of souls, and a guide to an end not enclosed within the bounds of this present life. Now he can never fully correspond if he is not well versed in the science of divine and sacred things, if he is not furnished with that piety which makes a man of God; and if he does not take every care to render his teachings valuable by the efficacy of his example, conformably to the admonition given to the sacred pastor by the Prince of the Apostles: "Forma facti gregis ex animo."For those who watch the times and the changeable condition of society, these are the right and the greatest gifts that could shine in the Catholic priest, together with the principles of faith; every other quality natural and human would certainly be commendable, but would not have with regard to the sacerdotal office anything but secondary and relative importance. If, therefore, it is reasonable and just that the clergy should accommodate themselves as far as is permitted to the needs of the present age, it is still more necessary that the present depravity of the century should not be yielded to, but strongly resisted; and this while corresponding naturally to the high end of the priesthood, will also render their ministry still more fruitful by increasing its dignity, and therefore gaining it respect. It is seen everywhere how the spirit of naturalism tends to penetrate every part of the social body, even the most healthy; a spirit which fills the minds with pride and causes them to rebel against every authority; depraves the heart and turns it after the desire of earthly goods, neglecting those eternal.
It is greatly to be feared that some influence of this spirit, so evil, and already so widely diffused, might insinuate itself even among ecclesiastics, particularly among those of less experience. What sad effects would not arise if that gravity of conduct which belongs to the priest, should be in any way lessened; if he should yield with lightness to the charm of every novelty; if he should deport himself with pretentious indocility towards his superiors; if he should lose that weight and measure in discussion which is so necessary, particularly in matters of faith and morals.
Would it not be a still more deplorable thing, causing as it would the ruin of Christian people, if he, in the sacred ministry of the pulpit, should introduce language not conformable to his character of a preacher of the Gospel? Moved by such considerations we feel it our duty again and still more warningly to recommend that above all things the Seminaries should with jealous care keep up a proper spirit with regard to the education of the mind as well as to that of the heart. They must never lose sight of the fact that they are exclusively destined to prepare young men not for merely human offices, however praiseworthy and honorable, but for that higher mission, which we lately spoke of, as ministers of Christ and dispensers of the mysteries of God. From such a reflection altogether supernatural, it will be easy, as we have already said in our Encyclical to the clergy of France, dated September 8, 1899, to draw precious rules, not merely for the correct education of clerics, but also to remove far from the institutes in which they are educated, every danger, whether external or internal, or of a moral or religious order.
With respect to the studies, in order that the clergy should not be strangers to the advancement of all good discipline, everything that is truly useful or good will be recognized in the new methods; every age can contribute to the knowledge of human learning. However, we desire that on this subject, great attention shall be paid to our prescriptions regarding the study of classic literature., principally philosophy, theology, and the like sciences-prescriptions which we have given in many writings, chiefly in the above-mentioned Encyclical, of which we send you an extract, together with the present. It would certainly be desirable that the young ecclesiastics should all follow the course of studies always under the shadow of the sacred institutes. However, as grave reasons sometimes render it necessary that some of them should frequent the public universities, let it not be forgotten with what and how great caution bishops should permit this.
We desire likewise that they should insist on the faithful observance of the rules contained in a still more recent document, which in a particular manner regards the lectures on anything else that could give occasion to the young men to take part in external agitations. Thus the students of the seminaries, treasuring up this time, so precious and full of the greatest tranquillity for their souls, will be able to devote themselves entirely to those studies which will render them fitted for the grand duties of the priesthood, particularly that of the ministry of preaching and the confessional. They should reflect well on the gravity of the responsibilities of those priests who in spite of the great need of the Christian people neglect to devote themselves to the exercise of the sacred ministry, and of those also who, not bringing to it an enlightened zeal for both the one and the other, correspond sadly with their vocation in things which are of the greatest importance in the salvation of souls.
Here we must call your attention, venerable brethren, to the special instruction which we wish given regarding the ministry of the Divine Word;and from which we desire they should draw copious fruit. With respect to the ministry of the confession: let them remember how severe are the words of the most enlightened and mildest of moralists towards those who, without purifying their own souls, do not hesitate to seat themselves in the tribunal of Penance, and how not less severe is the lament of the late great Pontiff, Benedict XIV., who numbers among the greatest calamities of the Church the defect in confessors of a science, both theological and moral, added to the gravity that such a holy office requires.
To the noble end of preparing worthy ministers of the Lord, it is necessary, venerable brethrens to watch with an ever-increasing vigor and vigilance not only over the scientific instruction, but also over the disciplinary and educative systems of your seminaries. Do not accept young men other than those who exhibit well-founded desires of consecrating themselves for ever to the ecclesiastical ministry.Keep them removed from contact and still more from living together with youths who are not aspiring to the sacred ministry. Such intercourse may, for certain just and grave reasons, be allowed for a time, and with great caution, until they can be properly provided for according to the spirit of ecclesiastical discipline. Those who during the course of their education shall manifest tendencies little suited to the priestly vocation, must be dismissed, and in admitting clerics to the sacred orders the utmost discretion must be used, according to the grave admonition of St. Paul to Timothy, "Manus cito nemini imposueris." In this matter it is only right that every consideration should be put on one side that is inferior to the most important one of the dignity of the sacred ministry. It is, therefore, of the greatest importance that in order to render the pupils of the sanctuary living images of Jesus Christ (which is the end of ecclesiastical education), that the directors and teachers should unite to the diligent fulfilment of their office the example of a truly priestly life. The exemplary conduct of those in authority is, especially to young men, the most eloquent and persuasive language to inspire in their souls the conviction of their own duties and the love of virtue."
You can read the full encyclical here