(b) The Duty of Renewal of the Hosts.—The consecrated species kept for Communion and adoration should be frequently renewed, lest they be corrupted. It would be a serious sin of irreverence to neglect this duty for over one or two months, or even for a shorter time if the danger of corruption is great on account of local conditions, such as dampness (Canon 1272).
(c) The Duty of Worship.—Pastors and others in charge of religious instruction should encourage devotion to the Eucharist, and especially the practice of assistance at Mass even on weekdays and of visits to the Blessed Sacrament. Benediction may be given frequently, and at least once a year there should be held in every parish church the Devotion of the Forty Hours, or at least some more solemn exposition of the Blessed Sacrament for a number of hours (Canons 1273-1275).
2709. The Sacrifice of the Mass.—In the Eucharist is contained not only a Sacrament which confers the grace of spiritual nutrition on its recipients, but also a sacrifice which offers to God Christ’s oblation as an act of adoration, thanksgiving, satisfaction and intercession. It is this sacrifice—which is one with the sacrifice of the cross, though offered unbloodily—that is known as the Mass. The chief persons who have duties in reference to the Mass are the celebrant and the assistants.
(a) The celebrant is the priest, who acts in the name and person of Christ. To say Mass validly one must have the power of Orders conferred in the presbyterate or priesthood, and must intend to consecrate (see 2701 b); to say Mass licitly one must be free from impediments which debar from Mass, such as suspension or irregularity. Strange priests who wish to say Mass are required to present a celebret or testimonial letter to the rector of the church (Canon 804), without prejudice, however, to their right to say Mass once or twice when they present themselves in clerical garb and sign the visiting priest’s book.
(b) The assistants are all those who hear Mass. Their duties were already explained in the question on the first precept of the Church (2576 sqq.). We shall confine ourselves here, therefore, to the duties of the celebrant.
2710. The Obligation of Saying Mass.—(a) The Obligation by reason of Orders or Priesthood.—Divine law imposes on priests as a body a grave obligation of celebrating Mass with such frequency that the memory of Christ’s passion be kept alive, which is the purpose of the priesthood, according to the words: “Do this in commemoration of Me.” Divine law also imposes on each individual priest the obligation of saying Mass at frequent intervals (i.e., at least, it would seem, on the greater feasts and at dates not more than six months apart); for a priest is ordained primarily to give glory to God and to impart blessings to man by the Sacrifice of the Mass (Heb., v. 1). It seems, therefore, that a priest receives grace in vain or neglects the sacrifice (II Cor., vi. 1, II Mach., iv. 14) if he omits Mass on the most solemn occasions of the year when nearly all the faithful are accustomed to receive Communion, or if he omits it for such a notable period as more than six months. It seems that the sin is _per se_ venial, as being opposed to fervor rather than to charity; but it may be mortal _per accidens_, as when serious scandal is given. There is no sin, however, if a priest has no opportunity to celebrate, or is lawfully impeded (e.g., on account of humility, scrupulosity, illness, or censure). The law of the Church recalls this obligation in Canon 805, and calls on bishops and religious superiors to exhort their subjects to say Mass at least on all Sundays and holydays. Daily Mass is quite customary today, and there might be serious scandal if without reason Mass were said only exceptionally.
(b) The Obligation by Reason of Special Offices or Duties.—Pastors are bound to say or provide Mass for their people on days of obligation as a duty of justice, and it seems on other days also as a duty of charity if there is a great need or demand and no reasonable impediment. There is an obligation of justice to celebrate Mass, if one has contracted to do so; an obligation of fidelity, if one has freely promised; an obligation of religion, if one has vowed; an obligation of obedience, if one has been lawfully commanded by one’s superior.
2711. Dispositions for the Celebration of Mass.—(a) Dispositions of Soul.—The celebrant must be in the state of grace, and must go to confession before Mass if he has a serious sin on his conscience (see 2701 c). He must have the intention and attention which the validity of the consecration requires (2701 b), and the reverence and devotion which is due the prayers of the Mass (2153 sqq.), Voluntary and fully deliberate distractions entertained for a considerable time during the Canon seem to be seriously sinful. It is most suitable, though apparently not commanded by the Church, that Matins and Lauds be said before Mass. There is, however, a duty of religion and of charity to self to make a suitable preparation and thanksgiving; but negligence here is a light sin, unless there be contempt or serious scandal. Fifteen minutes or a half-hour is recommended by ascetical writers, and the prayers may be taken from those given in the Breviary and Missal, Internal prayer, however, is more important than external recitation (Canon 810).
(b) Dispositions of Body.—The Eucharistic or natural fast is of grave obligation for the celebration of Mass (Canon 808). The only excuses are necessity according to divine law or exemption by ecclesiastical law. Necessity occurs when one must complete the sacrifice (e.g., when after the Communion the priest notices that he consecrated one species invalidly), or must avoid scandal (e.g., when a priest remembers after going to the altar that he is not fasting), or must consecrate for the Viaticum (e.g., when there is no consecrated host for a dying person). Since the law is ecclesiastical, the Church could dispense for a grave reason (e.g., to enable a sickly priest to say Masses on Sunday at widely separated points of his missions). It is clear that the celebration of Mass calls for cleanness of body, suitableness of dress, neatness and rubrical correctness of vestments (Canon 811). The omission of a principal vestment (i.e., blessed alb, stole or chasuble) is a serious sin, except in grave necessity; the omission of minor vestments (e.g., amice) is a venial sin, unless there is a just reason. The color of the day is not gravely obligatory, except by reason of scandal, and a good reason makes it lawful to use another color.
2712. Gravity of Regulations Concerning Circumstances of Mass.—Serious disrespect or serious scandal is caused by disregard of important regulations concerning the circumstances of the Mass. Hence, the following rules oblige under grave sin, though exceptions are permitted for cases of grave or very grave necessity.