I dont get how that "Once saved always saved" work

. Then again, I am a Roman Catholic.
Because we know the attributes of God include 'knowing the future", when Jesus died for our sins, He knew them all before we became "saved", right?
And, when Jesus died for our sins, we were not yet born, so the sins He died for were ALL in the future, right? So, if He died for my sins, then they were all in the future.
So, if God knows my future, then how could it be that I could get saved if I ever did anything that was soooo bad that He wouldn't die for it?
Is there anything that is more important than the cross? I don't think so!
Is there anything worse than murdering Chrisitans for because of their faith? Paul did that.
Also, when you read the Old Testament scriptures that say, "God is going to do this..." and it is about the wiping away of man's sins, He says stuff like this:
"...as far as east is from west, that is how far away he removes sin from me"
"...I will forgive their iniquity*, and remember their sins no more."
"...All we like sheep have gone astray; we have turned every one to his own way; and the LORD hath laid on him the iniquity of us all."
* "iniquity" is the propensity to do sin, like a tendency, to continually do it, to return to it.
CivGeneral, you need to read some Colossions, Philippinans, Ephesians, Romans. All these concepts are very vividly explained there.
"Who shall lay a charge against God's people?
29For whom he did foreknow, he also did predestinate to be conformed to the image of his Son, that he might be the firstborn among many brethren.
30Moreover whom he did predestinate, them he also called: and whom he called, them he also justified: and whom he justified, them he also glorified.
31What shall we then say to these things? If God be for us, who can be against us?
32He that spared not his own Son, but delivered him up for us all, how shall he not with him also freely give us all things?
33Who shall lay any thing to the charge of God's elect? It is God that justifieth.
34Who is he that condemneth? It is Christ that died, yea rather, that is risen again, who is even at the right hand of God, who also maketh intercession for us.
There is no one that exists who can lay a charge against God's elect.
If God justified (acquitted) us because Jesus' death, who is left?
Jesus said this:
And I give unto them eternal life; and they shall never perish, neither shall any man pluck them out of my hand.
My Father, which gave them me, is greater than all; and no man is able to pluck them out of my Father's hand.
There are many, many groups that claim Jesus but they do not believe He is who He said He is, they think him an ET, or a reincarnation of Buddha, and deny He is the Son of God.
Jesus will not deny those who truly belong to Him.