"Is missing Mass a mortal sin?"
Anon asked, “Is missing mass a mortal sin? My college age son was recently home and came to mass with me. When he didn't receive communion I asked him why. He said that he had missed mass the Sunday before and therefore wasn't allowed to receive communion if he hadn't gone to confession. Since I never miss mass I can't remember the rules here.” First of all, tell your son, "good job!" Not for missing Mass, but for his respect of the Eucharist. It’s great that he knows the guidelines for receiving Holy Communion, especially with regards to mortal sin.
I have taught four classes or religion to our junior high students in the past two school days. This question came up in each class, I think. One of the students even mentioned that another family member didn’t receive Holy Communion, and he asked why. I said to him that we really shouldn’t ask why someone didn’t receive Communion. That’s between them and God. I reiterated my respect for people who respect the Eucharist so much that they’ll run the risk of being judged by others because they don’t receive.
Missing Sunday Mass is a serious sin. If it involves full knowledge and full consent, then it is a mortal sin. Remember, all three conditions (grave offense, full knowledge, and full consent) have to be present for a sin to be a mortal sin. God says to “keep holy the Sabbath”. Jesus showed us how to worship the Father by gathering his friends around a table, and celebrating a meal. He commands us to “take this all of you and eat it…do this in memory of me”. As followers of Jesus, we are obligated, then, to keep holy the Sabbath by celebrating the Eucharist (Holy Mass). It is a grave obligation.
I think that most Catholics, if not all, who have use of right reason, know that they need to go to Mass each Sunday. Is it full knowledge? Probably not. In other words, I don’t think too many Catholics really know in full about the history and importance of the Mass, the theology of the Eucharist, the moral implications involved with the Commandments, etc. Once someone enters into a deeper understanding of the Mass and its central place in the Christian life, then one moves closer to full knowledge.
Finally, one has to freely choose to skip Mass on a Sunday (or Holy Day of Obligation) for it to be a mortal sin. When someone is physically unable to get to Mass (e.g., illness, no transportation), they are not freely choosing to miss Mass. In these rare cases, they are “dispensed” from the obligation. They should watch a “Mass for Shut-Ins” on television, if possible, so that they participate in some way with the Church in the liturgy on that day.
When I counsel people about observing the Sunday obligation, I remind them of the main reason that we have to be at Mass each Sunday: to receive the Eucharist. Jesus commands us to partake of the Eucharistic feast and that we need the Eucharist to have eternal life. I tell them that I really can’t imagine them saying for 24 straight hours on a Sunday, “No, Jesus, I don’t need to receive the Eucharist”. That’s essentially what happens when one knowingly and freely chooses to skip Sunday Mass.