10:9
That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved.
10:10
For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation.
Nothing in my Catholic past ever mentioned this.
And I notice that you conveniently skipped over Galatians.
Gal. 5:4 - Paul teaches that we can be in Christ, then be severed from Him and fall away from God's grace. You cannot be severed from something unless you were previously connected to it.