I am currently working my way through the Book of Concord. As I read through the Creed of Athanasius I questioned the last part about giving account of our deeds and that those who have done good deeds will have eternal life and those who have done evil will go into eternal fire. Isn't this contrary to the basis of Christian faith of salvation through grace in Jesus Christ?
What a wonderful and worthwhile reading project you have! Your question is one that many people ask when they read the Athanasian Creed. Your question also demonstrates the value of providing an explanation—in the service folder or by way of verbal announcement—when congregations use the Athanasian Creed in a worship service.
The section of the creed you cited reflects the language of Scripture regarding God’s judgment of humanity (Matthew 16:27; John 5:28-29; Romans 2:6-10; 2 Corinthians 5:10). God certainly judges what is in the heart. It is faith in Jesus Christ alone that saves, and it is unbelief that condemns (Mark 16:16). Salvation is entirely God’s doing; we do not contribute to our salvation in any way (Romans 3:28; Galatians 3:11; Ephesians 2:8-9).
What Scripture does explain is that saving faith and condemning unbelief manifest themselves in people’s lives. And so on the last day, the Lord will point out the good works that Christians have done and the sins that unbelievers have committed (Matthew 25:31-46). Those good works of Christians were not the payment for their salvation; the good works were the evidence of Spirit-worked saving faith in Jesus who paid the penalty for their sins. The sins of unbelievers will be singled out because they rejected the only means of forgiveness for their sins.
What the parable of the sheep and the goats illustrates is that God will demonstrate how fair a judge he is. He judges what is in the heart. A person cannot see into the heart of another as God can, so God will provide the evidence for the judgment of the heart that he made.
Once again, that parable shows us that on the last day no sins of believers will be brought up. That is because there are no sins to bring up; Christians enjoy complete forgiveness of sins through faith in Christ. On the other hand, the sins of unbelievers will be mentioned because they cannot do good works (Romans 14:23) and, because they have rejected the only means of forgiveness, their sins condemn them.
We could think of the section in the Athanasian Creed (“Those who have done good will enter eternal life, but those who have done evil will go into eternal fire.”) this way: “Those who believed in Jesus as their Savior—and saving faith always produces visible fruit—will enter eternal life, but those who rejected Jesus—such people cannot perform good works, nor do they enjoy forgiveness of sins—will go into eternal fire.”
Keep up your reading and study!