Why will Satan be released after being confined for a thousand years?
Satan will be released after the thousand-year confinement in order to test the final population of that thousand-year time. This release is necessary for that testing after the millennium, for he must be loosed to test that final population; the purpose is to test them.
Les teaches that Satan is confined for the thousand years, but then he must be released in order to test the final population of that thousand-year time. This release serves as a test for those who lived through the millennium. In the surrounding passage, verse 4 of chapter 20 describes thrones, with judgment meaning rule, given to them, and the souls of those beheaded for the witness of Jesus who had not worshipped the beast or received his mark. They lived and reigned with Christ a thousand years. So the release of Satan after the thousand years is for the purpose of testing that final population.