Q. To fulfill the Sunday obligation to attend Mass, how long or for what parts must you be present? What is the penitential rite? Must you be present for that? When may you leave and still fulfill the obligation? If you left for the homily or while Communion was being distributed, then returned, would you fulfill the obligation?
A. The present Code of Canon Law reads: “On Sundays and other holy days of obligation the faithful are bound to participate in the Mass.” It doesn’t say part or parts of the Mass. The expectation is that the person will attend a complete Mass. A Catholic Catechism quotes the canon and states, “Those who deliberately fail in this obligation commit a grave sin.”
Before Vatican II, moral theologians and canonists would talk about the three principal parts of Mass as the Offertory, Consecration and Communion. If you missed any one of those parts, they wrote, you would not have fulfilled the obligation of hearing Mass.
Today, canonists and liturgists do not use that terminology. They speak of the gathering, the Liturgy of the Word, the Liturgy of the Eucharist and the commissioning as the main divisions of Mass.
And moralists are more likely to speak of substantial observance of the law and what that might mean. They would assert that the law imposes a serious obligation. But some would question whether a person seriously or gravely violates the law if on one occasion he or she does not attend Sunday Mass. And all moralists would acknowledge that to miss a few minutes would not be a serious matter.
If you look at your missalette or recall your experience on Sundays, the penitential rite is part of the Mass. It takes place after the entrance song, right after the priest has entered the sanctuary and greeted the people. It can take different forms. One commonly used is the confession of fault (confiteor) and Lord, have mercy (Kyrie, eleison). So if you come after these prayers, you are late for Mass.
Just as there can be excuses for missing Mass, there could be excuses for coming late or leaving early or missing part of the celebration. A parent might have to take a crying child from the church. A person may feel ill or need to use the restroom. There would be no fault in leaving for such reasons. But to sneak a cigarette or step outside because of boredom would hardly be sufficient causes.
A hospital worker may have to leave early or a mother may have to hurry home to watch children while Dad takes a turn at going to Mass. A traveler may have to make a bus or plane. Surely such reasons would excuse from fault. But to be first out of the parking lot, no!
While an emergency may demand that a person leave before the end of Mass, one who has departed before the consecration and Communion can hardly be said to have attended Mass. But the emergency may excuse that person from further effort to go to Mass.