Is it really a mortal sin to skip Sunday Mass?

Pope Innocent XI has condemned the following proposition: "The precept of keeping Holy Days is not obligatory under pain of mortal sin, aside from scandal, if contempt is absent." (4 March 1679)

Thus, it is the teaching of the Catholic Church, that it is always a mortal sin intentionally to skip Mass on Sunday or on a Holy Day without a serious reason. Catholics are obligated to attend Mass either on Sunday itself, or on the Saturday evening before.

Let us consider the proof of this precept, and show the falsity of the contrary opinion that it is enough usually to go to Mass on Sundays and Holy Days, and that skipping only one Sunday here or there is merely a venial sin.

The authority of St Alphonsus

The doctor of moral theology and patron of confessors, St Alphonsus Liguori, states simply (quoting Pope Innocent XI) that the precept of attending Mass on Sundays and Holy Days (as well as abstaining from unnecessary servile work) binds under pain of mortal sin.

The reader can find his treatment of this in Theologia Moralis, Tomus Primus, 263ff.

According to the current law of the Church, this obligation is fulfilled by attending Mass any time from the preceding evening until midnight of the day – thus, a Saturday evening Mass (whether for the Sunday or for the Saturday, or a wedding Mass, etc) will fulfill the Sunday obligation.

This is, however, a positive precept, rather than a negative one. This is significant since there can be no exceptions to negative precepts – there is never a case when a man is permitted to commit adultery or to lie, for example. However, a man may be excused from positive precepts for a serious cause.

Therefore, there are certainly circumstances which would excuse a man from attending Sunday Mass – as the obligation is grave, only a grave cause could excuse. However, certain grave circumstances do exist.

In this article, however, we will not consider the various exceptions to the law, but rather the basic obligation of the law.

We only point out that we have  used the phrase "skip" Sunday Mass, rather than "miss" – thereby we indicate the difference between missing Mass for a grave reason (e.g. being in the ER at the hospital) and skipping Mass for no good reason (e.g. simply sleeping in).

The obvious bad will in those who say skipping Sunday Mass is not a grave sin

Note that those who advocate for the opposite opinion (namely, that it is only a venial sin to skip Sunday Mass on occasion) fail to quote a single Church document or even the opinion of any saint to support their impious claim. We can see here the bad will of such persons, who promote their own opinion and the vanity of the world in the place of the true doctrine presented by our Holy Mother the Church.

The Catechism of the Catholic Church specifies that attending Mass on Sundays and Holy Days is a precept of the Church (cf CCC 2180) which precepts are given to maintain the bare minimum of moral rectitude (cf CCC 2041, "the very necessary minimum").

Again, "The faithful are obliged to participate in the Eucharist on days of obligation, unless excused for a serious reason (for example, illness, the care of infants) or dispensed by their own pastor. Those who deliberately fail in this obligation commit grave sin." (CCC 2181)

Again, the Baltimore Catechism: "Holydays of obligation are special feasts of the Church on which we are bound, under pain of mortal sin, to hear Mass and to keep from servile or bodily labors when it can be done without great loss or inconvenience. Whoever, on account of their circumstances, cannot give up work on holydays of obligation should make every effort to hear Mass and should also explain in confession the necessity of working on holydays." (No 3, q.1244)

Therefore, whosoever should rashly and with such great hubris dare to assert and even to teach others that occasionally skipping Sunday Mass or Holy Days for no grave reason is not a mortal sin, is rightly to be held in contempt by all and should know himself to be guilty of spiritual murder as leading others into sin, himself having certainly committed grave sin by his impious utterance.

This especially holds for priests.

What makes "grave matter" to be a "mortal sin"?

A sin is mortal if it is grave matter, and committed freely and knowingly.

Clearly, skipping Sunday Mass is grave matter. However, we will not here discuss when a person may or may not have sufficient knowledge or freedom for the sin to be mortal – that is better done in the confessional with a devout and traditional priest.

It is good here to recall that the Catechism teaches that "anyone conscious of a grave sin must receive the Sacrament of Reconciliation before coming to Communion." (CCC 1385) 

[please note, I have made a correction to the above section to make it more clear that "grave sin" means "mortal sin", and that the distinction is between objectively "grave matter" and "mortal/grave/serious sin" -- thanks to Kevin L who helped to point out this error]

Why is it a mortal sin to skip Mass on Sunday?

The great St John Paul II states, “The Code of Canon Law of 1917 for the first time gathered this tradition into a universal law. The present Code reiterates this, saying that ‘on Sundays and other holy days of obligation the faithful are bound to attend Mass’. This legislation has normally been understood as entailing a grave obligation: this is the teaching of the Catechism of the Catholic Church, and it is easy to understand why if we keep in mind how vital Sunday is for the Christian life.” (Dies Domini, 47)

Here, the Saintly Pontiff indicates why it is that the Church obliges the faithful to attend Mass on Sundays and Holy Days under pain of mortal sin: Mass attendance is truly necessary for the Christian life. Participating in Sunday worship is of such great value and necessity to the soul, that the Church holds the faithful bound to this participation by a grave obligation.

We must admit that the following of this precept is of the greatest advantage to the Christian soul which will quickly perish without the helps of common worship, orthodox preaching, and the grace derived from the Sacrament of the Altar.

Furthermore, we must stress that it is the primary duty of the creature to honor his Creator. If God had commanded that every day should be given wholly to him, he would have been within his rights – for the whole man, together with all his time and energies, belongs entirely to God. However, God is most generous in demanding (through his Church) only Sundays and a very few other days which must be given to divine worship. It is such a small demand in his part, and those who fail to do even this little amount are guilty of an extreme boldness.

There can be no doubt that those who fail in this most basic duty of man have failed to fulfill even the bare minimum of what is required of any decent human being – therefore, it is good and right that the Church should hold the faithful bound to the observance of Sundays and Holy Days under pain of mortal sin.