Some Protestant denominations claim that salvation is a one time thing, that once one confesses they accept Christ as their Lord and Savior that they are saved from the depths of Hell for all eternity. That nothing they do on Earth, after this confession, has any role in their admittance into Heaven. But unfortunately for those who believe in this false teaching, "Once Saved, Always Saved" (the common name for this belief) is not found in Scripture*.
*As Catholic Christians, we do NOT believe that everything needs to be written explicitly in Scripture for it to be true. That is a Protestant, man-made belief. Although we as Catholics do NOT believe in the Bible Alone teaching, we can understand the teaching of "Once Saved, Always Saved" is a direct contradiction to what Scripture actually teaches us about salvation and therefore is NOT true (on the basis that is NOT taught in Scripture, and that is directly contradicts Scripture).
What does Scripture teach us about salvation?
Well firstly, the Church teaches us that we are saved by God's grace, but it is through our cooperation in God's grace through the act of faith and works that we accept his gift of grace (CCC 2010).
Scripture then goes on to teach us that our cooperation in this grace, plays a role in our salvation. We learn that this cooperation is our act of faith and works. Verses such as James 2:14-26 we learn that Faith and Works go hand-in-hand. That faith alone, or more commonly phrased as "salvation by faith alone" (or 'sola-fide') is not a Biblical teaching. In fact, it is contrary to Scripture where we learn that we are NOT saved by faith alone. We are taught this in verses such as: James 2:14-26, Matthew 19:16-17, Romans 2:1-11, 1 Corinthians 15:1-2, 2 Corinthians 11:15, 1 Peter 1:17, Romans 20:12-13, and many other verses.
Now that we know that Faith and Works are necessary, let us look at another thing Scripture teaches us about salvation.
Scripture teaches us that salvation is a process, and is NOT a one time thing. Proving that salvation is a process totally disproves the man-made Protestant teaching that "once you're saved, you're always saved".
We know that salvation is a past event (Romans 8:24, Ephesians 2:5, Ephesians 2:8, 2 Timothy 1:9, Titus 3:5, 1 Corinthians 6:11), a present event (Philippians 2:12, 1 Peter 1:9), and a future event (Matthew 10:22, Matthew 24:13, Mark 8:35, Acts 15:11, Romans 5:9-10, Romans 13:11, 1 Corinthians 3:15, 1 Corinthians 5:5, Hebrews 9:28).
But doesn't Scripture teach us that we are saved simply by believing in Christ being our Savior that we are saved?
No, Scripture does NOT teach this. Belief is an essential part in our acceptance and cooperation in the gift of grace. But Scripture does note that belief is not simply enough. In verses such as Matthew 7:21-23 we are taught that “'Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but only the one who does the will of my Father in heaven. Many will say to me on that day, ‘Lord, Lord, did we not prophesy in your name? Did we not drive out demons in your name? Did we not do mighty deeds in your name?’ Then I will declare to them solemnly, ‘I never knew you. Depart from me, you evildoers.’"
Is Salvation something that can be lost?
Since we understand that salvation is a process, and our cooperation in the gift of grace is necessary, we can take note that salvation can be lost on Earth. We will go over the verses that teach this shortly, but before we do, let us clarify something. In this belief that salvation can be lost on Earth, we are not saying it can be lost in Heaven. Once you are in Heaven with God, you are IN HEAVEN WITH GOD. What we are noting, from Scripture, that reception or acceptance of this salvation on Earth is not final until the end. We learn that we can move away from God, separate ourselves from Him (on Earth), even after confessing our faith. We learn this in verses such as Romans 11:22-23, 1 Corinthians 10:11-12, Galatian 5:4, Philippians 3:8-14, 1 Timothy 4:1, 1 Timothy 5:15, Hebrews 3:12-14 and many other verses.
Looking at all the verses mentioned in this article, we can understand that the Protestant belief of 'Once Saved, Always Saved' is contrary to Scripture. Scripture instead teaches us that Salvation is a process, that you CAN separate yourselves from Christ (even after proclaiming your Faith), and that faith and works are the way in which we cooperate with the grace God has gifted us.