Justification is one of, if not the most, disputed topics between Catholics and Protestants. There is a basic agreement that faith is necessary, but agreement stops there. Many Protestants believe that once faith in Jesus is accepted, a person is saved. The Catholic Church teaches that faith is necessary, but works are also necessary as a demonstration of that faith. Even if a person professes his belief in God, he can still lose his soul by failing to live a life pleasing to God.
Faith and Works/Can Lose Salvation in the Bible
There are many places in the New Testament which speak of faith and works as necessary together. “You see that a man is justified by works and not by faith alone. And in the same way was not also Rahab the harlot justified by works when she received the messengers, and sent them out another way? For as the body apart from the spirit is dead, so faith apart from works is dead.” - James 2: 24 – 26. In this passage, James clearly lays out that faith and works are both necessary. “Note then the kindness and the severity of God: severity toward those who have fallen, but God's kindness to you, provided you continue in his kindness; otherwise you too will be cut off.” - Romans 11:22. St. Paul speaks in this passage about how, if a person does not remain faithful to God, he will lose his salvation. “Do you not know that in a race all the runners compete, but only one receives the prize? So run that you may obtain it. Every athlete exercises self-control in all things. They do it to receive a perishable wreath, but we an imperishable. Well, I do not run aimlessly, I do not box as one beating the air, but I pommel my body and subdue it, lest after preaching to others I myself should be disqualified.” - 1 Corinthians 9: 24 – 27. This is a very striking passage, because St. Paul recognizes that he himself could not reach Heaven if he fails to live a good life. He had obviously already accepted faith in Jesus, after his dramatic experience on the road to Damascus, but he here demonstrates his knowledge and belief that that one profession of faith is not enough; he must continue to live a life in accordance with God so that he is not shut out of Heaven.
Faith and Works/Can Lose Salvation Early Church Fathers
The early Christian writers also understood and taught that faith and works are necessary
together in order to reach Heaven.
When we hear, 'Your faith has saved you,' we do not understand the Lord to say simply that they will be saved who have believed in whatever manner, even if works have not followed. To begin with, it was to the Jews alone that he spoke this phrase, who had lived in accord with the law and blamelessly and who had lacked only faith in the Lord. - Clement of Alexandria Stromateis or Miscellanies 6:14:108:4
Whoever dies in his sins, even if he profess to believe in Christ, does not truly believe in him; and even if that which exists without works be called faith, such faith is dead in itself, as we read in the epistle bearing the name of James. – Origen Commentaries on John 19:6
Certain ones of those [Gnostics] who hold different opinions misuse these passages. They essentially destroy free will by introducing ruined natures incapable of salvation and by introducing others as being saved in such a way that they cannot be lost. - Origen De Principiis Book 3 Ch. 1.8
Paul, joining righteousness to faith and weaving them together, constructs of them the breastplates for the infantryman, armoring the soldier properly and safely on both sides. A soldier cannot be considered safely armored when either shield is disjoined from the other. Faith without works of justice is not sufficient for salvation; neither is righteous living secure in itself of salvation, if it is disjoined from faith. - Gregory of Nyssa Homilies on Ecclesiastes 8
He that believes in the Son has everlasting life. Is it enough, then, to believe in the Son,' someone will say, 'in order to have everlasting life?' By no means! Listen to Christ declare this himself when he says, 'Not everyone who says to me, "Lord! Lord!" shall enter into the kingdom of heaven'. - John Chrysostom Homilies on the Gospel of John 31:1
Only let not Christ be forsaken, so that THE LOSS OF SALVATION and of an eternal home would be feared. - Cyprian Treatise 3 Ch. 10
The world returned to sin…and so it is destined to fire. So is the man who after baptism renews his sins. - Tertullian On Baptism Ch. 8
These writers clearly believe and articulate that faith and works are together necessary for salvation. Once a person professes his faith, he can still lose his salvation if he falls into serious sin and does not live in accordance with God's laws. A person's way of life is of equal importance with their belief in God.