Lose, no. Reject, yes. Here is the Joint Declaration on the Doctrine of Justification by Catholics (1999), Lutherans (1999), and Methodists (2006): By grace alone, in faith in Christ's saving work and not because of any merit on our part, we are accepted by God and receive the Holy Spirit, who renews our hearts while equipping us and calling us to good works. http://www.vatican.va/roman_curia/pontifical_councils/chrstuni/documents/rc_pc_chrstuni_doc_31101999_cath-luth-joint-declaration_en.html However Catholics do not believe in once saved, always saved. Saved Christians have the freedom to fully reject God and their salvation. We call this mortal sin. 1 John 5:16-17 - If any man see his brother sin a sin which is not unto death, he shall ask, and he shall give him life for them that sin not unto death. There is a sin unto death: I do not say that he shall pray for it. All unrighteousness is sin: and there is a sin not unto death. Matthew 18:7-9: Woe to the world because of things that cause sin! Such things must come, but woe to the one through whom they come! If your hand or foot causes you to sin, cut it off and throw it away. It is better for you to enter into life maimed or crippled than with two hands or two feet to be thrown into eternal fire. And if your eye causes you to sin, tear it out and throw it away. It is better for you to enter into life with one eye than with two eyes to be thrown into fiery Gehenna. (Matthew 18:7-9) If one is "once saved, always saved" then these verses would have no meaning to Christians. The parable of the Good Samaritan also teaches us about the sin of omission, not doing something that morally we should do. The priest and the Levite are examples of "saved" people who are committing serious sins of omission. See Luke 10:30-37. Were the 12 Apostles "saved"? Prior to his betrayal of Jesus Christ, was Judas Iscariot "saved"? The Bible seems to infer that Judas went to Hell: "Woe to that man who betrays the Son of Man! It would be better for him if he had not been born" (Mark 14:21). "Once saved, always saved" Christians would say "No, Judas was never really saved." Like the rest of the Apostles, Judas was called and chosen by Jesus and left everything behind to follow the Lord. He called Jesus "Lord" (Savior was still yet to come). For three years he followed the Lord with the other Apostles. These are the acts of a "saved" Christian. In Mark 6:7-13, Jesus sends forth the 12 Apostles (including Judas) and they "drove out many demons, and they anointed with oil many who were sick and cured them." How could an "unsaved" Judas accomplish this? Catholics would argue that Judas was "saved" when he was sent forth but that committed mortal sin when he betrayed Jesus and committed suicide. Luke 6:16 lists the Apostles "... and Judas Iscariot, who became a traitor." Judas was "saved" and through his own free will committed mortal sin and threw away his salvation. With love in Christ.