Is it possible for a Christian to lose salvation?

TL;DR:

A Christians cannot lose their salvation. God has promised to keep us, and He cannot fail in His redeeming, sanctifying work in the heart of the believer.

Scripture teaches that a true believer cannot lose his or her salvation. According to the Bible, Christians are those who by faith, have personally received and fully trusted in Jesus Christ as the only Savior from sin (John 3:16–18; Acts 16:31; Ephesians 2:1–10). As a result, that person has been freed from eternal condemnation, been made new, and been given the indwelling Holy Spirit (2 Corinthians 5:17–21; Ephesians 1:3–14). Scripture presents several reasons it is impossible for such a person to lose salvation.

Ephesians 2:8–9 makes it clear that true, saving faith is the gift of God. For salvation to be lost, God would have to take back His gift. God does not lie or go back on His promises (Numbers 23:19; Romans 11:29). Therefore, the gift of faith He imparts to His own will never be taken back. God won't allow us to lose our salvation, for the sake of His name, His character, and His glory.

Secondly, the Christian is a new creation (2 Corinthians 5:17). The power for the new creation comes from God, not from us. Just as we had no hand in our first birth, we have no hand in our rebirth (John 3:3). We are God's creation, and for a Christian to lose salvation, God would have to cancel and reverse the new creation.

Scripture teaches justification, the doctrine that explains what happens at salvation. To be justified means to be declared righteous by God by virtue of the exchange that happened at the cross (Romans 5:1). Our sin was exchanged for the righteousness of Christ (2 Corinthians 5:21). For a Christian to lose salvation, God would have to go back on His Word and "un-declare" what He had previously declared and take back the righteousness of Christ. That simply doesn't happen.

God promises eternal life to all who come to Christ (John 3:16). Eternal life is just that—eternal, forever. For a Christian to lose salvation, eternal life would not be eternal. Again, God will not break His promise by taking away that which He has declared to be eternal. Jesus made a profound statement about the security of the believer in John 10:28: "I give them eternal life, and they will never perish, and no one can snatch them out of my hand."

Those who object to the belief that a Christian cannot lose salvation point to professing Christians who continue to live in sin and those who become Christians and walk away from the faith. It could be that such people are in a period of wandering (1 Corinthians 3:13–15; Galatians 6:1–5; 1 Thessalonians 5:14; James 5:19–20). Though they are faithless, God will remain faithful (2 Timothy 2:13). Another possibility is that these people are merely professing Christians but do not actually have a relationship with God through Christ (1 John 2:19). We cannot judge another’s heart, so when we see a professing Christian stray, we should pray and continue sharing the truth of the gospel.

from the old testament

The Bible shows that love and faithfulness are God’s most abiding traits. Many of the Psalms show that God remains with His people and loves them even when they stray from Him (Psalm 86:15, 89:33, 100:5).
No one can change God’s plans (Isaiah 14:27), so if He saves us no one—even us—can change that. We are etched in the palm of His hands (Isaiah 49:15-16)

from the new testament

John 10:28 records Jesus saying, “I give them eternal life, and they will never perish, and no one will snatch them out of my hand.” No one is more powerful than God. No one can take away what He gives us.
Jesus promises to “never cast us out” those who come to Him (John 6:37).
The apostle Paul listed anything that could threaten humankind, but indicated that none of those things could separate believers from God: “For I am sure that neither death nor life, nor angels nor rulers, nor things present nor things to come, nor powers, nor height nor depth, nor anything else in all creation, will be able to separate us from the love of God in Christ Jesus our Lord” (Romans 8:38-39). We are Christ and He is ours—for eternity.
Since salvation is the work of God alone, we don’t have the power to remove it (Ephesians 2:8-9).

implications for today

What do these things have in common: car keys, foot races, reading glasses, patience?

They can all be lost. And some of those losses have worse consequences than others. But nothing could be as terrifying as the thought of losing eternal salvation. It’s as if you’ve started to drown, were thrown a life jacket . . . only for that jacket to deflate when you finally get it on.

Thankfully, if you’re a true believer, you cannot lose your salvation. That’s because you weren’t saved by your own effort. Christ’s work, not ours, saves us, and no one can undo what the Lord has done. That should make us confident that whatever sin we commit, we can confess it to Him and be forgiven (1 John 1:9). It should also compel us to share this good news with others so that they can have the same assurance we have.

Jude 1:24-25 says it all: "Now to him who is able to keep you from stumbling and to present you blameless before the presence of his glory with great joy, to the only God, our Savior, through Jesus Christ our Lord, be glory, majesty, dominion, and authority, before all time and now and forever. Amen."

understand

True believers cannot lose their salvation.
Christ saved us, so no one can override what He has done.
Be become new creations in Christ, and that compels us to live for Him.

reflect

Have you ever been afraid that you’ve sinned so egregiously that you’ve lost your salvation? If so, how did you overcome such feelings?
How does the security you feel in Christ impact your relationship with the Lord?
How does the fact that your salvation is secure impact how you share the good news with others?

engage

What impact might the message of eternal security have on those who come from works-based religious traditions?
What do we learn about God’s character from the Bible’s teaching on eternal salvation?
Fears abound in today’s world. How can the message of eternal salvation be a balm to those fears?