If salvation is by grace alone, why are the dead judged according to their works?

Christian doctrine—particularly in Protestant traditions—teaches that salvation is by grace alone through faith (e.g., Ephesians 2:8-9). However, Revelation 20:12 states that the dead are "judged according to what they had done as recorded in the books." How do Christians reconcile salvation by grace with a final judgment based on works? If our works don’t contribute to our salvation, what is their role in the judgment described in Revelation and similar passages?