On 3rd May, 1858, in the second of two Encyclicals on the Clergy in that year, Bl. Pius IX issued an Encyclical on Priests and the Care of Souls, entitled Amantissimi Redemptoris:
"4. Nothing is greater or holier than the unbloody sacrifice of the Mass, in which the body and blood of Christ are offered to God for the salvation of all. Holy Mother the Church has always been careful and diligent in order that the Mass be celebrated by priests with clean and pure hearts. It should be celebrated with the proper splendor of sacred ceremonies and rites so that the greatness of this mystery will shine forth all the more even from external appearances. This will also arouse the faithful to the contemplation of divine things hidden in such an admirable and venerable sacrifice. And with like solicitude and devotion, the same most holy Mother has never ceased to urge, exhort, and influence her faithful sons to frequently attend this divine sacrifice with due piety, veneration and devotion. She teaches that they must at all cost be present at it on all holy days of obligation, with their minds and eyes religiously intent on that from which the divine mercy and an abundance of all good things might be acquired.
"5. The sacrifice of the Mass must be offered by pastors of souls for the people committed to their care; this obligation comes from a divine precept according to the teachings of the Council of Trent, since the same Council teaches in most express and grave words: "it is by divine mandate that all those to whom the care of souls is committed are to know their sheep and offer sacrifice for them." The encyclical letter of Benedict XIV of 19 August 1744 speaks most wisely about this obligation, explaining and confirming more fully the mind of the Fathers of Trent. In order to remove all controversies, questions, and uncertainties, he clearly declares that pastors and all others actually having the care of souls ought to offer the sacrifice of the Mass for the people committed to them on all Sundays, and holy days of obligation, as well as on those days on which he, lessening the number of holy days of obligation in some dioceses, allowed people to engage in servile work, with the provision that the faithful fulfill the obligation of hearing holy Mass."