Why would God threaten believers with punishment for failure to attend mass? The most plausible justification, at least initially, is that he wants to encourage them to attend, in the same way that a parent punishes a child who skips school. The problem is that God inflicts a punishment identical to the harm to be avoided in the first place! We can presume that God wants believers to attend mass with the ultimate goal of saving their souls from damnation; the danger in not attending mass regularly is that one may stop believing and/or commit acts which are inherently wrong such as murder, theft or adultery and end up in hell. But threatening believers with the potential danger is absurd, as it unnecessarily increases the danger which believers face, giving them an easier and more certain avenue to hell. (Of course, hell itself is already infinitely unjust. Of course, God himself created the original danger. I’m just showing how it’s absurdity upon absurdity.) It would be as though the state executed drivers who failed to use their seat belts. That’ll show them to be more careful next time! Never mind that there’s no next time, either for the executed or the damned, and that they would have been perfectly fine without either punishment.
Of course, if God has purely selfish motives for demanding his believers worship him every week, we might have a different analysis. One might think that God, for every person he tosses into the everlasting flames, loses an infinity of worship from this person, but St. Thomas Aquinas argued the saved in heaven will delight in the suffering of the damned, so perhaps God’s interests are served no matter what. Then why go the whole charade of earthly existence? I would say that perhaps the drama is interesting, but God already knows how it’s going to end anyway. What’s the point of playing it out? It’s impossible to avoid absurd conclusions when one postulates an infinite being, and throwing in infinite rewards and infinite punishments doesn’t help. My intention here was just to point out one additional absurdity peculiar to Catholicism.