Long post, but I hope you read what I’ve written.
“How exactly do they leave?” As always, I get the sense that there’s something hidden in your question. But that indelible mark will be there, CMatt, when you face your judge, and no, it cannot be erased from your soul, anymore than unrepentant sins can. Haven’t those who have physically left by their non-participation in weekly liturgy and abandonment of the sacraments also spiritually left as well? They have freely turned their backs to the Church, - their total being, body and soul. Is that not “leaving?” No doubt there will be many baptized Catholics in hell, and I’ve often wondered if that mark of Baptism could very well serve to not only save, but to condemn as well, because of the rejection of that which holds eternal life, but of course, that’s just me speculating on the realm that belongs to Christ alone. And for those unsure? Are you going to go through your entire life sitting on the fence when the answers (albeit not the ones you want to hear) have already been given? Perhaps it’s not answers you need or even want, but faith in the word of God and a submission of mind, heart and will to the One providing those answers. Sincere struggle is one thing and certainly grace will be given if asked for, but indifference to the gift which has been already been given, is as hostile to the message of Christ as is outright attack against His Church. “I will spew the lukewarm out of My mouth…”
Another point is that a gift has been supernaturally given to Catholics who have embraced truth. Sensus fidei (sense of the faithful) keeps us from erring – it is a discernment of truth which cannot separate itself from the teaching Magisterium of the Church (led by the Spirit.) Think of the early Christians….newly baptized in their faith and being told by dissident bishops that Christ was not divine. Oh, how they knew better (because of FAITH) and they could, at that point, not dissent even though they knew they might face certain death. Heresy and a split from authentic teaching is simply not an option. And please remember the words of AB Sheen, “Catholics need to be merciless to the error in the minds of heretics” because that is the highest form of charity.
Now a question for you. (Next post.)