Many, particularly in Protestant Denominations, believe that if they are “saved” once, often by publicly “accepting Jesus”, that they are always saved. “I don’t have to worry about anything that I do. I’ve been saved for all time because I have been saved many years ago when I accepted the Lord into my heart.”
Catholic Fundamentalists, as usual, compare the soul to a computer disc. We realize that a disc can be corrupted, no matter how clean it may have once been. Similarly, the “ether disc” that is the soul, though cleansed by Baptism or conversion, may also be later corrupted. The corruption of a “saved soul” is harder to get clean again. It can be done, and often is, but it is better to avoid sin in the first place. Thinking that having once been saved provides a “free pass” that allows us to go on sinning is one of the worst sins we can commit.