Wow, this is a thread full of overcorrection and overzealousness.
Ideally, a person attending Mass attends the entire Mass, from beginning to end. And it is praiseworthy and pious to be in church praying before Mass, at least 15 minutes ahead of time; it is also praiseworthy and pious to spend at least five minutes of prayer after Mass, thanking the Lord for His great goodness to us. If you’re living a placid life and the crick doesn’t rise, that shouldn’t be a problem.
HOWEVER.
In the real world, Mother Church gives an extremely generous interpretation of canon law, so that Catholics do not become discouraged and skip Mass altogether if they are a few minutes late to Mass in a strange town, or if the car won’t start on time, or traffic is heavy, or a doctor gets called out of church on an emergency, or their boss insists they work on Sunday, or whatever else happens to happen. In fact, the usual interpretation given to Catholics is actually less generous than the “official” one. (Most people in this country go with the old Irish teaching that you had to be there before the Gospel reading was done. And that’s not a bad rule of thumb, but the teaching in Rome was actually the more generous one. As Father Z once noted, that attendance cutoff was one reason for the ringing of the Offertory bell.)
The Church did not need to make official pronouncements in the Catechism of the Catholic Church, or in a papal bull. The ordinary magisterium is more than sufficient for the implementation of canon law and moral law. If it’s good enough for defining murder, it’s good enough for going to Mass. And no, the pre-Vatican II manualists were not dealing with a totally different situation. (If you believe that the Mass is the Mass, that is.) And don’t go looking to our Eastern Catholic brethren for a more severe interpretation in their canon law, because you won’t find it. Their ideas on Mass attendance are also quite generous, partly because their Masses are even longer.
To fulfil the Mass obligation, you have to attend the Liturgy of the Word and the Liturgy of the Eucharist. The Liturgy of the Word part is fulfilled if you get there even as late as the Offertory, that being the end of the Liturgy of the Word. (Yup, you don’t even technically have to be there for the Gospel.) The Liturgy of the Eucharist part is fulfilled by being there until Communion - in fact, until the priest receives Communion. That’s the barest bare bones of Mass, but you can get out of there without any bad conscience if you really have to go.
You can even fulfill the Mass obligation by being present at one part each, divided over two Masses. (In case you get there just in time for the Liturgy of the Eucharist, but can stay for the Liturgy of the Word at the next Mass. Or vice versa, if the day is very weird.)
Obviously, these generous provisions are supposed to be used for emergencies or hardship situations. Obviously some people abuse that generosity; but their lack of generosity to Christ doesn’t mean that the Church needs to tighten up and be mean to the people using them wisely.
Abusing the rules is a loss to the person doing it, and serves as its own punishment. If a person knows that he was late because of laziness and neglect, he knows he’s not prepared for Communion even if he made it on time to hit the obligation. But that’s a Catholic person’s own responsibility to discern, as part of discerning the Body of Christ. It’s not the job of random people to discern that for him.
…
And yes, I’m one of those Catholics who is not only there every week, but is there really early doing stuff or praying. At my old parish, I often ended up assisting at more than one Mass in the morning as part of helping out with music and other stuff. I’m gung ho about Mass attendance. But I know my rights under canon law, and I respect those of others.
(And if it’s a daily Mass that isn’t for a Holy Day of Obligation, getting there late is not something to fret too much about. Not ideal, not a good plan, but not sinful or bad.)