Genuine questions on why it is a sin to leave the Catholic Church
I recently learned it is a sin to leave the Catholic Church...perhaps I knew this, but forgot. I am aware that not going to Mass is a sin, marriage to non-Catholics is not possible, etc. However, this one intrigues me.
I have a number if questions and genuinely seek to understand, not challenge any status quo...it is an educational moment for me (and perhaps others).
EDIT: I did post to r/AskAPriest...they removed it and said to post here.
Assume a person is leaving the Catholic Church is going to a different denimination (Baptist, Lutheran, etc.), is still a believer and follower of Christ. They remain a Christian; however, they are told this is a sin.
1. Is it s grave sin or mortal sin?
2. Aren't we all Children of God, regardless of our religious Christian affiliation?
3. Related to that, how does the Church view indifferentism?
4. They follow same God, same Jesus, same Bible, same path to Heaven through Jesus. What is different?
5. They are Baptized in the Trinity. Again, what is different?
6. Does apostasy truly count? They are not abandoning their Christian faith, but rather moving denominations.
7. Is it still a sin, despite the Catholic Church teaching we must follow our informed conscience?
8. What paragraph(s) in the CCC can I read more on this specific sin?
9. Assuming this is based on Biblical Theology, what Bible verses are there where I can read about this specific sin?