63 But the most efficacious means of apostolate among the poor and lowly is the priest's example, the practice of all those sacerdotal virtues which We have described in Our Encyclical Ad Catholici Sacerdotii. Especially needful, however, for the present situation is the shining example of a life which is humble, poor and disinterested, in imitation of a Divine Master Who could say to the world with divine simplicity: "The foxes have holes and the birds of the air nests, but the Son of Man hath not where to lay His head." A priest who is really poor and disinterested in the Gospel sense may work among his flock marvels recalling a Saint Vincent de Paul, a Cure of Ars, a Cottolengo, a Don Bosco and so many others; while an avaricious and selfish priest, as We have noted in the above mentioned Encyclical, even though he should not plunge with Judas to the abyss of treason, will never be more than empty "sounding brass" and useless "tinkling cymbal." Too often, indeed, he will be a hindrance rather than an instrument of grace in the midst of his people. Furthermore, where a secular priest or religious is obliged by his office to administer temporal property, let him remember that he is not only to observe scrupulously all that charity and justice prescribe, but that he has a special obligation to conduct himself in very truth as a father of the poor.
Source: Divini Redemptoris (Vatican.va)