Pope Pius XII On Vocations

The choice of candidates for the priesthood recommended by Canon Law to pastors of souls must be the particular task of all priests, who have not only to render humble and generous thanks to God for the inestimable gift they have received but in like manner must hold nothing dearer or more pleasing than to find and prepare a successor for themselves among those young men whom they know to be equipped with the necessary qualifications. To succeed more efficaciously in this, every priest must make an effort to be and to show himself an example of the priestly life which for the young men whom he approaches and among whom he looks for signs of the divine call can constitute an ideal for imitation.

This wise and prudent selection must go on always and in all places not only among the young men who are already in the seminary but also among those who are studying elsewhere, and particularly among those who partake in the various activities of the Catholic apostolate. These last, even though they enter the priesthood at a later age, are often equipped with greater and more solid virtues because they have already been tried and have strengthened their souls by contact with the difficulties of life and have already collaborated in a field which is also the realm of priestly activity.
MENTI NOSTRAE (Apostolic Exhortation To The Clergy Of The Entire World On the Development of Holiness in Priestly Life) Pius XII