There are likely multiple misunderstandings here.
In general… the original question shows a very immature understanding of what Catholics actually believe. In short, these questions seem to be MORE aimed at Protestant or non-denominational Christians who have a more black n white understanding of Salvation.
What Catholics typically refer to as “Sola Fide” or “faith alone”
FIRST understand that Catholics do not believe in “faith alone” NOR in a black n white idea of: “believe in God or go to hell”
But as I said, there are multiple issues here. I’m going to focus on just 1
Why make the punishment for what people do in their life infinitely disproportional to what they have done…?
In our own justice system… WHAT was done, is not as important as WHOM is harmed. Think about this for a moment and let it sink in…
Kill a person = Bad
Kill a Child = VERY Bad
Kill an Officer in the line of duty = EXTREMELY Bad
Kill the President = WORSE STILL, possibly an act of war if you are a foreigner.
In each situation, a single life was taken. What was DONE remained the same…technically.
But in each WHO was harmed changed and it is THIS that our own justice system weighs even more so then what was done.
Let’s look at the President issue - or ANY leader of a country, really, Why is killing him/her any worse then a Police Officer? Cynically, we may even argue that the Police officer does MORE on a daily basis to make there country better. - OK, so why is the President worse then the others… it’s just 1 life. RIGHT?
Because the President represents us ALL. To kill him… is to attack us all, because that is what he represents. It is not the MAN that you harm…but the position or title.
Now continue to ramp this up, first 10 fold, then 100 fold, the a million, then a billion, keep going, slowly 'til you get to an INFINITE god. – To the MOST supreme being and who has no limits. What you harmed is not a finite being… 1 single entity. It is what that represents or what it IS.
In Christianity, God is not another being it the Universe. God is love itself. Justice itself, BEING itself, Freewill itself. God is not a thing or a representation of a thing…but the THING itself. Goodness itself.
What you harm or rebel against is not simply God…but what he is.
If the President represents ideas like Freedom, Democracy, Justice, etc. And so killing him is an afront to all of that. How bad is it to stick a knife in Love itself, Freedom itself, Justice itself… not a mere representation of the thing…but the very nature of the thing??
WHAT would be an adequate punishment for such a being who harms the very nature and reality of everything good?.. how long would it take to pay back that offense?
In our justice system… the most we can extract from a person is their life. Either life in prison OR death.
Now what if there is no time AND the life is eternal? - “Houston, we have a problem!”
How do we atone or apologize for something that severe without time or physical death?
Now you COULD say that if God is merciful, loving, and not evil, that he’d simply forgive us. TRUE!
And that is the part of Christian theology that Atheists largely ignore.
But what if the person does not WANT to be forgiven either because they don’t see that they have caused any offense OR feel justified in what they did? - then what?
Obviously you’d have to FIRST believe there is a God to begin with, or else none of the above matters.
So FIRST try and resolve your issue with whether or not there is a God to begin with.
Not argue the finer points of theology… if you aren’t FIRST vested in the idea of God to begin with.
First step is to realize that “God” is a title… not a proper name. It is a word like any other to describe something that fits a series of roles or criteria.
People also refer to God as:
The “uncaused cause”
The “unmoved mover”
“First Cause”
“esene” or “being” itself.
The most supreme being
“love itself”
“Mercy itself”
The model for which concepts like Logic, Justice, Love, etc. came from.
If you have not already, start with Thomas Acquainas’ 5 Ways - really 5 arguments FOR the existence of God - not proofs.