Dear Deacon:

We are obligated to attend Sunday Liturgy each Sunday (which means Sunday Mass, or the Sunday Vigil Mass on Saturday) unless there are legitimate reasons why we cannot (such as illness, required work, etc.) For travel, it depends. I know that when I have traveled, I will stop in some town and attend Mass, then continue on my way. But, if this is not possible, then travel can be a valid reason.

The Church began offering the Sunday Vigil Mass on Saturday evening to accommodate those who must work on Sundays. It is perfectly legitimate to attend the Vigil Mass when it is not possible to attend the Mass on Sunday.

While it is still technically permissible to attend the Vigil instead of the Mass on Sunday, there are many who abuse this accommodation by attending the Vigil so they can keep Sunday for themselves. Sunday is the Lord's Day, not our "fix the roof" day.

The Vigil Mass is allowed because it looks back on the Jewish custom of the day beginning on the evening of the previous day. Thus, according to this custom, Sunday begins at sunset on Saturday and continues until sunset on Sunday. Thus, in reality, those who attend the Sunday Vigil ought to consider the evening of Saturday to the evening of Sunday as the time frame that they practice their Sabbath (no unnecessary work, worship of God, rest and recreation with family, etc.)

Even if the Vigil Mass accommodation is abused, it is still licit, thus no grave sin is committed. As for Venial sin, because of the motivation to keep Sunday to oneself? Perhaps, but that that is between the person and God.

God Bless,
Bro. Ignatius Mary