Since I am not Christian, let alone Catholic, I intend to ask questions that normally couldn’t be asked on Christianity Stack Exchange. That website is really intended for fact-based questions on Christianity, not “Truth questions”. Truth questions are something like “Is X a sin?” As you might have guessed, this thread is asking just about that: whether refusing to listen to the priest’s sermon a sin.
Without looking at the Catechism (I’ll be surprised if it’s actually in there word-for-word!), I think such a behavior would be characterized as a sin, because it involves some free will to refuse something that is intended to aid spiritual growth. If refusing to listen to your mother or father is disrespectful, then the same logic can be applied to the priest, can it not? However, does disrespect automatically make something a sin? And if it’s a sin, would it be classified as a mortal sin (something that would probably deserve confession) or venial sin?
On the subject of Roman Catholic hamartiology, is something a sin because a person feels guilty of a behavior, or is something a sin because of a biblical narrative or because it is mentioned by one of the Church Fathers?