“IN CHRIST” is your key here. What does it mean to be IN CHRIST to Catholics? And how does one get IN CHRIST?
But for the 25 words or less answer ... I'm not sure I can do one!
Christ comes into our lives and draws us into his life, by his Spirit into Himself. An early climax of this narrative is represented by "the sinner's prayer." But I don't think it starts there or is utterly fulfilled there.
Now I ask again:
You do know that we teach that those "in purgatory" are already saved, right? The 'works' done in purgation do not lead to salvation,they result from it.It is, I think, too simple to disparage "Faith + works = salvation." That's why I think James wrote the line we quote, and why Paul wrote this and the whole thing in Philippians. Faith + works in some sense ≠ salvation, but salvation sure has works in it.