Human good works play a tremendously important role. There can be no salvation whatsoever without good works, and your good works are crucial to your salvation. Now, how can a Protestant make a statement like that?
First of all, good works are absolutely crucial and are, indeed, necessary for salvation because God requires good works to save anybody. Those good works are supplied and provided by Christ, who in His perfect humanity earned the infinite merit of God—the reward of which is the very basis of my salvation. Without Christ’s righteousness, I am in very big trouble. So my salvation, initially, is grounded upon good works—Jesus' good works.
What about my own good works? Do they have a role? Most Protestants would say no. Justification is only one part of salvation. Salvation is the big word. Salvation is the word that covers all of the process by which God fully brings us to total redemption. Justification is that point in the process when God declares me a person who is in a state of redemption. The fact is that you are already justified, and you are in a state of salvation to a degree, but there's still more of your salvation yet to come. You still haven’t gone to heaven. You still haven't been perfectly sanctified. You haven't been glorified. None of those things will happen to you until you die and go to heaven. When you die and go to heaven, God will give you a reward for whatever degree of obedience you have rendered to Him in your Christian life. The reward that God bestows upon you in heaven will be given according to your works but not because your works are so righteous and meritorious that they impose an obligation upon God to reward them. God has graciously given us the promise that He will reward whatever obedience we give Him. He doesn't have to, but out of His goodness and grace, as Augustine said, 'He crowns His own gifts.' Our entrance into heaven is strictly by the righteousness of Christ. Our reward in heaven will be granted according to the works of obedience that we render.
"What role does human achievement or good works play in salvation?" and other questions can be found in our Questions Answered section. You can also download the free ebook What Does It Mean to Be Born Again? by R.C. Sproul.