14 Regarding the requirements of a perfect priestly formation and education, it is necessary that seminarians be induced, tactfully but firmly, to espouse those virtues which are the prime qualification of the priestly calling, "that is, the duty to achieve personal sanctification." (26) The newly-ordained native clergy of those countries must enter into pious competition with the clergy of those old dioceses which have long been producing priests in their midst who were such mirrors of virtue that they are proposed as examples to the clergy of the whole Church. In fact, it is through sanctity that priests can and must be the light of the world and the salt of the earth. (27) In other words, they can, especially by their sanctity, show their own countrymen and the whole world the beauty and the supernatural power of the Gospel; they can teach all men that a perfect Christian life is a goal toward which all of God's children must strive, struggling and persevering with all their strength, regardless of their place of birth, their walk of life, or the degree of civilization they enjoy.
Source: Princeps Pastorum (Vatican.va)