The doctrine of purgatory places an emphasis on our own merits to attain righteousness.
It is a very dangerous thing to add to the finished work of Christ, but this is precisely what millions of people do when they accept the doctrine of purgatory. Purgatory is the belief that there is an intermediate state after physical death where people undergo purification, so as to achieve the holiness necessary to enter the joy of heaven. However, to hold to this doctrine you must deny the power of the cross, and distort the gospel.
First, the only righteousness that merits eternal life is the imputed righteousness purchased through Christ’s atoning death on the cross. Paul says, “God made him who had no sin to be sin for us, so that in him we might become the righteousness of God” (2 Cor. 5:21). Those who put their faith in Christ get His perfect righteousness credited to them. Writing to the church at Philippi, the apostle Paul says, “What is more, I consider everything a loss because of the surpassing worth of knowing Christ Jesus my Lord, for whose sake I have lost all things. I consider them garbage, that I may gain Christ and be found in him, not having a righteousness of my own that comes from the law, but that which is through faith in Christ—the righteousness that comes from God on the basis of faith” (Phil. 3:8-9).
However, the doctrine of purgatory places an emphasis on our own merits to attain righteousness. Therefore, righteousness doesn’t come from God on the basis of faith (as Paul clearly states), but comes as a result of penance and suffering. This is a salvation based on works, not faith.
This destroys the consistent message of the New Testament that “it is by grace you have been saved, through faith—and this is not from yourselves, it is the gift of God—not by works, so that no one can boast” (Eph. 2:8-9). Grace is unmerited; it’s undeserved. That is why we call it good news.
Second, my eternal and secure confidence before God is enjoyed now, and cannot be taken away, even by death itself. Paul writes, “Therefore, there is now no condemnation for those who are in Christ Jesus . . .” (Rom. 8:1). That little word “now” is extremely significant. Those who are in Christ can have confidence right now that they are redeemed. In Colossians, Paul writes, “For he has rescued us from the dominion of darkness and brought us into the kingdom of the Son he loves, in whom we have redemption, the forgiveness of sins” (Col. 1:13-14). Notice again, we have redemption now. We have forgiveness of sin now. The rescue mission is over. He has rescued us. It is finished.
Purgatory runs counter to Paul’s explicit teaching. If the doctrine were true, then the blood of Jesus is not enough to cleanse our sins. Something extra is needed. But that denies the power of the blood of Christ. What can wash away my sin? Nothing but the blood of Jesus.