58 Therefore, Venerable Brethren, it is necessary that the priest, even among the absorbing tasks of his charge, and ever with a view to it, should continue his theological studies with unremitting zeal. The knowledge acquired at the seminary is indeed a sufficient foundation with which to begin; but it must be grasped more thoroughly, and perfected by an ever-increasing knowledge and understanding of the sacred sciences. Herein is the source of effective preaching and of influence over the souls of others. Yet even more is required. The dignity of the office he holds and the maintenance of a becoming respect and esteem among the people, which helps so much in his pastoral work, demand more than purely ecclesiastical learning. The priest must be graced by no less knowledge and culture than is usual among well-bred and well-educated people of his day. This is to say that he must be healthily modern, as is the Church, which is at home in all times and all places, and adapts itself to all; which blesses and furthers all healthy initiative and has no fear of the progress, even the most daring progress, of science; if only it be true science.
Source: Ad Catholici Sacerdotii (Vatican.va)