I'm sure that Stella, as well as the other Roman Catholics in this forum, was never been taught in Roman Catholicism that even Paul had to come to the point where he saw that all his achievements and good works were worthless in God's eyes, and that he was nothing more than a bankrupt sinner with a proud heart. He therefore had to turn from all his good works and his high estimate of himself. He came to Jesus Christ with empty hands, to cast himself on His mercy and to receive salvation. He himself had not achieved it. It had been achieved for him. Paul therefore abandoned any attempt to save himself and trusted completely in Jesus Christ. In other words, he turned from self-righteousness to Jesus as Saviour. In so turning he received the perfect righteousness of Jesus as a precious gift.
Furthermore, this salvation cannot be earned. Nor can it be merited by human works. It must be received as a gift of God based solely upon His mercy and grace: "To the one who does not work, but believes in Him who justifies the ungodly, his faith is reckoned as righteousness." (Romans 4:5)