10 For this reason We earnestly exhort all priests of the secular clergy to let the faithful see them following the Spiritual Exercises, at least in that modest measure which the Code of Canon Law prescribes for them: and let them approach and fulfil the exercises with an ardent desire of their own perfection, so that they may obtain that abundance of the supernatural spirit, which is very necessary for them, if they would secure the spiritual advantage of their flock, and win a multitude of souls to Christ. For this was the path trodden by all those priests who, burning with zeal for the salvation of souls, were foremost in guiding their neighbours on the way to holiness, and in educating the clergy; as may be seen, to take a recent example, in B. Joseph Cafasso, to whom We ourselves decreed the honours of the blessed in Heaven. For it was the constant custom of this most holy man to labour assiduously in the Spiritual Exercises, in order that, by this means, he might better nourish his own sanctity, and that of other ministers of Christ, and might know the heavenly counsels. And once, when he came forth from a sacred retreat, gifted with divine light, he clearly showed this same path to a younger priest, whose confessor he was; and he followed it up to the highest summit of sanctity. This was the blessed John Bosco, whose name is beyond all praise. As for those who, under whatever title, serve within the bounds of religious discipline; since they are commanded by law to make the sacred exercises every year there can be no doubt that they will bring from these sacred retreats an abundance of heavenly goods for which, as each one needs, they may draw draughts of greater perfection, and all the graces enabling them to run the way of the evangelical counsels with alacrity. For the annual Exercises are the mystical "tree of life" by which both individuals and communities may live in that fame of sanctity, in which every religious family must needs flourish. Nor should the priests of the Clergy, secular and regular, think that the time spent on the Spiritual Exercises tends to the detriment of the apostolic ministry. On this matter, let them hear St. Bernard, who did not hesitate to write thus to the Supreme Pontiff, Blessed Eugene II, whose master he had been: "If thou wouldst belong wholly to all, after the manner of him who became all things to all men; I praise thy humanity, provided it be full. But, how is it full when thou art excluded? Thou also art a man: therefore, that the humanity may be whole and full, let it gather thee also into the bosom which receives all: else, what will it profit, if thou gain all, and lost thyself? Wherefore, when all have thee, be thyself one of them that have. Remember, I say not always, I say not often, but at least sometimes, to render thyself to thyself."
Source: Mens Nostra (Vatican.va)