Why is missing Mass on Sunday a mortal sin?

My son is asking why missing Mass on Sunday (without serious cause) is a mortal sin. He does not see how it passes the “grave matter” requirement for something to be a mortal sin. He is comparing it to other sins such as murder, and cannot understand how it could be in the same category. Can you please explain it?

The following links should help you better understand the Church’s teaching on missing Mass. If you have any further questions, please contact Catholic Answers directly.

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[LIST]
*]Why is skipping Sunday Mass a mortal sin?
*] Are there any exceptions for missing Mass?
*]Is Confession needed when missing Mass?
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