Strawberry,
You nor any “professing” Christian can be assured of anything except death and taxes. Why do Christians believe the word of God is Truth? It is the only book in the world that actually and really transforms lives to be more like the image of the Creator. It cannot be understood nor believed without God indwelling a person; this is why you and others make silly statements that no one can know because from your point of view and from God’s you are correct just as god has said in His word.
If you want absolute proof of the authenticity of the Bible and can be summed up in a single word. Israel.
That tiny nation should not exist as many greater and mightier nation have come and gone, but God in His providence promised in his word to protect Israel and He has. Find me an Edomite, Sodomite, Geserite or a Hititie or any other powerful nation that has passed and no longer exists.
All men will one day know the veracity of Scripture; for most it will be too late and on your current path you will also fall into the majority. In fact the longer you stay in these forums and are exposed to the truth the more accountable you become and if you do not repent and come to the Lord, you will reap greater judgment on yourself according to the word of God.
We don’t pretend to know who will or won’t be saved. And we don’t speculate about anyone’s current standing with God. God is the judge, not us.
I understand your desire to convert someone you consider lost. You crossed the line when, rather than explaining your views on salvation, you speculated about another’s standing at the moment and used scare tactics by threatening eternal damnation.
As I said, Catholics don’t speculate about anyone’s salvation, and we certainly don’t threaten non-Christians with Hell!
Only God knows who is saved and who is damned. Who is any person to speculate about another–and with such certainty? Maybe it is the speculator types who will be surprised when those they are certain will be damned pass them on the way to the pearly gates.
There are little icons here that perfectly represent the OSAS and the I-know-who-isn’t-going-to-Heaven types when they realize (and are quite annoyed, I bet) that Heaven is populated (“polluted” in their holier-than-thou opinion) with the people they were sure were headed to Hell. You know - Catholics, Muslims, Communists, fans of the other team, drug addicts, alcoholics, and so many more undesireables. I want to be in heaven just to see the looks on their faces. Here they are.

followed by

and finally reaching

, before they admit that they aren’t God and couldn’t have known who was and wasn’t saved. Then, when they finally get it, they can relax, give up fear, and love their neighbors (rather than declare them damned). Then they will finally feel the Joy peace of God and will begin to greet their neigbors like this.
On a serious note - I wonder if this is the sin that most of us will spend more “time” in Purgatory over - lack of charity and love toward others. I think it is.