In 1959, for the 100th anniversary of St. John Mary Vianney’s death, Pope John XXIII gave the Church this encyclical, Sacerdotii Nostri Primordia. It is addressed to priests, but it provides all the faithful both insights on St. John Vianney’s life and wisdom for the spiritual life.
Pope John XXIII describes how St. John Vianney was rigorously ascetic, carrying out harsh penances for the sake of souls.
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. (no. 10)
The saint gave his life to the God and the Church in obedience and love:
It is said that St. John M. Vianney lived in the Church in such a way that he worked for it alone, and burned himself up like a piece of straw being consumed on fiery coals. (no. 33)
Just before this, and in view of St. John Vianney’s own obedience, John XXIII speaks on the importance of priestly obedience.
We are offering clerics this total obedience as a model, with full confidence that its force and beauty will lead them to strive for it more ardently. And if there should be someone who dares to cast doubt on the supreme importance of this virtue—as sometimes happens at the present time—let him take to heart these words of Our predecessor of happy memory, Pius XII, which everyone should keep firmly in mind: “The holiness of any life and the effectiveness of any apostolate has constant and faithful obedience to the hierarchy as its solid foundation, basis and support. ”
For, as you well know, Venerable Brethren, Our most recent predecessors have often issued serious warnings to priests about the extent of the dangers that are arising among the clergy from a growing carelessness about obedience with regard to the teaching authority of the Church, to the various ways and means of undertaking the apostolate, and to ecclesiastical discipline. (nos. 30–31)
Pope John XXIII also writes about the importance of prayer and devotion to the Eucharist.
This is how [St. John Vianney] taught his faithful to pray: “You do not need many words when you pray. We believe on faith that the good and gracious God is there in the tabernacle; we open our souls to Him; and feel happy that He allows us to come before Him; this is the best way to pray.” (no. 47)