10 You cannot begin to speak of St. John Mary Vianney without automatically calling to mind the picture of a priest who was outstanding in a unique way in voluntary affliction of his body; his only motives were the love of God and the desire for the salvation of the souls of his neighbors, and this led him to abstain almost completely from food and from sleep, to carry out the harshest kinds of penances, and to deny himself with great strength of soul. Of course, not all of the faithful are expected to adopt this kind of life; and yet divine providence has seen to it that there has never been a time when the Church did not have some pastors of souls of this kind who, under the inspiration of the Holy Spirit, did not hesitate for a moment to enter on this path, most of all because this way of life is particularly successful in bringing many men who have been drawn away by the allurement of error and vice back to the path of good living.
Source: Sacerdotii Nostri Primordia (Vatican.va)