Really? So, a Roman Catholic need only profess faith in Him, and that's it, eternity in Heaven is assured, no matter what?
If so, I've been misled regarding certain stuff like your "mortal sins" and "last rites" and praying people's souls out of "purgatory" (to name a few).
You've jumped from A to C.
Catholics and Reformed Christians both agree that Christ's blood is the only ransom for sin and Christ's merit is the only source of grace.
We disagree over whether the Scriptures teach that mere verbal profession is the means of availing ourselves of Christ's grace.
We believe that Christ meant what he said: "not everyone who says Lord, Lord will enter the kingdom of Heaven" but that he who does the will of the Father will be saved. We believe that a mere verbal profession can sometimes be empty and meaningless - "This people worships me with their lips but their hearts are far from me."
In other words, for the Catholic faith is not just a synonym for "belief" - having faith means being faithful.
I mean, quite honestly, what does it mean to you when Christ tells the Apostles that He will judge us on the Last Day by how we have served him?
I've never gotten a direct answer from a Reformed Christian about how we are to take such passages from the Gospels.