For Christians, justification by faith is important because it is unique. Every other system of belief, from the most divergent pantheistic religion to Christian cults that claim Jesus' name, denies that salvation is by faith in Jesus Christ. True Christianity that is based on Scripture must admit that justification by faith in Jesus is the only way to heaven (John 14:6). The Bible says that faith naturally produces works because of a changed heart and the indwelling Holy Spirit (a process called sanctification), but the Bible does not support the idea that justification happens by any other means than faith (Romans 5:1–5).
Why is the doctrine of justification by faith so important?
Justifcation by faith is also important because it gives us a correct view of ourselves and of God. To be justified means to be "pronounced righteous" or "treated as righteous." When a criminal is justified by the court, he stands innocent before the court. They have pronounced him not guilty. The problem is that mankind's only hope of being seen righteous by a holy God and Judge is to be totally perfect—something we all know is not possible, because Adam fell and took all men with him (1 Corinthians 15:22). Yet, God requires perfection (Matthew 5:48). This is a problem for all of us, because no one is righteous—not even one (Romans 3:12). God has required of us something that is impossible for us.
We also know that "by works of the law no human being will be justified in his sight, since through the law comes knowledge of sin" (Romans 3:20). This means that the Law was never meant to provide a way to salvation, but it was provided to make us realize that we needed a Savior. Which is why Paul goes on to say: "But now the righteousness of God has been manifested apart from the law, although the Law and the Prophets bear witness to it—the righteousness of God through faith in Jesus Christ for all who believe" (Romans 3:21–22a). This is the basic gospel, the good news that we do not have to be perfect, or provide salvation for ourselves, because the perfect Lamb of God has died to provide it for us. All we must do is believe that He is willing and able to save us. That is the essence of justification by faith.
So, knowing this, to believe that we are justified by works is a complete denial of biblical, orthodox Christian truth. God takes His gospel very seriously, and issues a stern warning to those who would teach people otherwise: "But even if we or an angel from heaven should preach to you a gospel contrary to the one we preached to you, let him be accursed. As we have said before, so now I say again: If anyone is preaching to you a gospel contrary to the one you received, let him be accursed" (Galatians 1:8–9).
What is justification according to the Bible?
Does the Bible teach eternal security?
Is salvation by faith or works or both?
Why do so many people believe in salvation by works?
How are good works the result of salvation?
Truth about Salvation