The entire Bible leads up to the last lines written by St. John in The Book of Revelation 22:15, right before The Epilogue. “These others must stay outside: dogs, fortune-tellers, and fornicators, and murderers, and idolaters, and everyone of false speech and false life.”
St. John makes it clear that not everyone will get into Heaven. Those who think otherwise want to get around the clear, direct meaning of his words.
Such people are included within another specific group not allowed in Heaven. They identified in Matthew 18:6. “If one of these little children believes in me, and someone causes that child to sin, it will be very bad for that person. It would be better for them to have a millstone tied around their neck and be drowned in the deep sea.”
How do these passages relate to Catholics and non-Catholics?
If a person leads anyone, including themselves, away from The Church, and dies unrepentant, they are “millstoned”. Forever.
Our current state of historical awareness is such that many Protestants do not know that The Only Church Jesus Founded was The Roman Catholic Church. Those who know that, and prefer some man-invented schism, must ask themselves: “Does worshiping in a man-invented schism while ignoring The Only Church Jesus Founded make me an idolater?”
If such a person says “No.” and refuses to think adequately about it, is he or she leading him or herself astray?
That a very important question.
The question is especially important for those who are smart enough to recognize the danger of being eternally “millstoned”, suffering endlessly the agony of being deprived of life-giving oxygen.
Who doesn’t get to Heaven? The millstoned.