A friend of mine posted a section of Casper Olevianus’ catechism about the final judgment: http://merekyle.blogspot.com/2009/11/caspar-olevianus-on-justification-and.html
Believer’s obedience and good works are still sullied with the stains of the flesh and are imperfect; much that is sinful still clings to their good works. Thus if their works were presented before the judgment seat of God, they would of necessity be liable to the sentence that God has already pronounced in His Word, “Cursed is everyone who does not continue in all things which are written in the book of the law, to do them (Gal. 3:13). It is, therefore, easy to see that if we should depend in part on our works, even a little, our consciences could never be at peace or assured that we are justified before God and can stand in His presence. Instead they would be assured of our condemnation.
170 Q: You are not saying, then, that good works are useless?
A: They do not serve to make us right with God, either wholly or in part, but they do serve this purpose: after we have been freely and graciously justified through the imputation of Christ’s righteousness, we show with good works that we are thankful to God the Lord, so that God might be praised through us. That is the reason we were originally created and then redeemed, as Zachariah teaches in Luke 1:74,75: “That we, being delivered from the hand of our enemies, might serve him without fear, in holiness and righteousness that is pleasing to him all the days of our life.”
Good works are also useful because by the example of our good works we win others to Christ and keep those already won from falling away. The longer they are kept close to Christ, the more they are built up.