My sister believes that it should not be a mortal sin to not go to Mass every week. What can I tell her to convince her otherwise?
You might politely ask her upon what authority she is basing her belief that not going to Mass every week should not be a mortal sin. Catholics believe that Christ entrusted his Church with the authority to teach, sanctify, and govern Christians in his name. Since the Church states that it *is *a mortal sin to deliberately miss Sunday Mass without just cause, that authority should be good enough for Catholics. To disregard the Church’s teaching authority and act instead upon one’s own authority is not a Catholic attitude.