53 But thanks be to God, it is just this flame of apostolic zeal which is one of the brightest jewels in the crown of the Catholic priesthood. Our heart fills with fatherly consolation at the sight of Our Brothers and Our beloved Sons, Bishops and Priests, who like chosen troops ever prompt to the call of their chief hasten to all outposts of this vast field. There they engage in the peaceful but bitter warfare of truth against error, of light against darkness, of the Kingdom of God against the kingdom of Satan.
Source: Ad Catholici Sacerdotii (Vatican.va)